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1. 2 Attempt to identify and eliminate any potentially likely residual flow paths during the tree building stages within Frank Wolfe so that any post assignment analyses may proceed as normal without worrying about possible residual paths In effect the first tries to cure the disease once it has occurred the second tries to inoculate against it A semi empirical method based on method 1 was initially introduced within SATURN release 10 9 and is described in the following section 15 57 4 However on further reflection it seems that the method 2 is far more promising but at present it has only been applied in preliminary stages See 15 57 5 The jury is still out 15 175 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 57 4 15 57 5 5120257 Apr 15 Section 15 Removing Residual Flows Post Assignment SATURN release 10 9 12 introduced two highly experimental applications which attempt to remove residual flows if they have occurred within the assignment 1 Calculating multiple commodity i e times distances and tolls O D skims in SATLOOK SKIM_ALL 15 27 7 2 Converting a UFC O D route format file into a UFO format file in SATALL 15 23 6 and 22 5 3 Since any path flow along a non minimum cost route is strictly speaking a residual flow it becomes important to establish a rule to identify an important residual flow which needs to be dealt with as opposed to the unimportant flo
2. 3 Both P1X 11 8 1 and SATDB 11 10 7 5 can repeat the assignments carried out in the assignment and select trips which either a pass through a selected node b pass through a selected sequence of nodes in order or c pass through one or more of a set of screen line links Option b includes the possibility of either identifying links by specifying two adjacent nodes or turns by identifying three nodes Option c further explained in 11 10 7 5 allows both conventional screen lines in the sense of a closed set of links surrounding a town centre or more generally any set of links The screen lines may be defined either using the link selection facility 11 6 1 or a set of 7777 input data records 6 10 in both P1X and SATDB P1X also offers two additional methods for defining screen lines interactively using the mouse or via an external data file 11 8 1 7 Those trips which satisfy the selection rules are re loaded and the total assignment pattern of trips before and after they pass through the selected node or nodes is displayed graphically or as a data base table P1X and SATDB have further options which duplicate those in SATU2 to either output a selected trip matrix UFM file 11 8 1 3 print a sector to sector trip matrix Generally speaking P1X is considerably easier to use than SATDB firstly through the use of mouse based link or node selection and secondly since the display of the s
3. 3 and 4 are generally saved on the SATURN UF files but 2 Is only in effect saved on a UFC file if the SAVEIT option is requested Trees may be built using any of the available times above The following notes describe the differences between these times in greater detail and suggest circumstances in which they might be used 1 Free flow times are defined within SATNET for all network elements e g links centroid connectors EXCEPT for simulation turns whose free flow times are the delays calculated by SATSIM with zero flow on each turn Free flow times are generally used to build the first set of trees in the assignment These may be thought of as the ideal routes 2 At each subsequent assignment iteration the times are set according to equations 5 1 where V is the current flow such that the assigned volumes at iteration i are used to set the times and therefore the costs at iteration i 1 15 60 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 24 4 5120257 Apr 15 Section 15 Therefore these times would be used to re construct the routes built at each stage of the assignment procedure they constitute the real routes as assigned N B The times as defined above are only preserved on a UFC file if SAVEIT T so that only then can actual routes be re created In actual fact what are saved are NOT the times but the costs i e including the fixed components appropriately weighte
4. 4 ZL hi 3 100 e E 11 95 1 0333 FRSOMIGR AY SLA not found not found 5170 196 5 3 0 oS 0 6 ff 1 4 503 6 3 3 our Fe 1 3 16 41 3 205 9 2 61 1 56 158 16 163 7 SATURN MANUAL V11 3 SATURN Special Options and Facilities Over capacity queues Link cruise times Total travel times Average speed Total delay Average delay per vehicle Average delay per vehicle kilometre Average trip length Average simulation queue Simulation queue at end of modelled time period and gt gt gt gt gt gt gt gt gt Turn penalties More detailed comparisons are available within the Summary worksheet by selecting the second level option to highlight more convergence statistics and for example performance for both the modelled hour and the next time period i Aria 10 vJB Z U B a n gt oh lE E D AWE f amp Congestion Index mins veh km Bm C Import CSW Mate Created 15 03 07 version 3 00 Network Bodge amp Doodle Stkins with Extended Sirstkins with Extended Sirktkins with Extended Si Matrix Original Original Development Original Development Original Development Zones Directory Assignment Cofvergence Summary for EPSOMSBAKX EPSOMSSRxX EPSOMSSRxXX EPSOMSSRxX QJ t b mn Cofvergence Statistics Om io 11 11 1 0 121 11 0 121 11 0 121 11 0 370 31 0 370 31 0 370 31
5. As noted in Section 5 5 4 it may be possible convenient to define bus flows as pre loaded flows or vice versa For example if you have a very large number of low frequency bus routes it may be simpler to simply aggregate all their individual flows by link turn and input them as fixed pre loaded flows rather than go through the hassle of defining individual routes as per 6 9 the impact on the assignment and with some reservations the simulation will be identical On the other hand bus flows may have certain properties that distinguish them from other flows e g bus lanes Equally coding buses as aggregate fixed flows means that you cannot analyse individual route timings etc 15 12 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 6 15 6 1 15 6 2 5120257 Apr 15 Section 15 Comparing Assigned and Observed Flows GEH Statistics General Options It is possible to obtain a number of goodness of fit statistics Comparing the modelled flows on both links and turns with observed counts in order to check the performance of the model This can be carried out in several ways The most comprehensive and flexible set of comparisons is available within P1X either under Validation 11 7 1 or SATLOOK 11 11 13 In these cases the observed flows are taken from the input ufs file as originally read as 77777 records in the network dat file The modelled flows may be defined in a number of different ways in order
6. Cordoning matrices within a sub network SATCH 12 1 Producing a PIJA file using SATPIJA 13 1 2 Producing a file of route flows SATPIG 12 6 Turning flows at buffer nodes 15 36 Producing cost and or skimmed matrices 15 27 In order to obtain the route flows necessary to carry out such analyses a parameter SAVEIT must be set to TRUE in the final assignment in SATALL or SATEASY most easily done by declaring it to be TRUE its default under amp PARAM in the DAT file input to SATNET There are then three different methods by which the O D route information is preserved under SAVEIT dependent mainly upon the assignment method MET used 1 Remembering the costs used on each Frank Wolfe iteration and their weights in order to be able to re construct each individual route by re building trees MET 0 only 2 Explicitly storing flows per individual O D route path path based assignment MET 1 only 3 Storing a bush of splitting factors per individual origin user class from which individual O D route flows may be calculated by a single pass OBA and or Frank Wolfe with extra steps added Methods 2 and 8 are generally considerably faster than method 1 in terms of route flow analyses but may require extra memory to store the required data and or extra CPU to create them in the first place The following 4 sub sections 15 23 2 through 15 23 5 deal exclusively with method 1 the eq
7. SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 free flow speed coded for each link and that there is no need to impose an extra travel time on them But if you do want to impose penalties on all user classes go right ahead The fact that the penalty is fixed means that it is included within the travel time for that user class under all conditions i e all soeeds and all flows To give a simple numerical example consider a link 1 km long with an input free flow speed of 120 kph which presumably applies to cars user class 1 but with user class 2 lorries having been assigned CLICKS 2 100 Under free flow conditions cars take 30 seconds to travel the 1 km at 120 kph lorries take 36 seconds at 100 kph Hence the fixed time penalty is 6 seconds for user class 2 The end effect is identical to adding a penalty of 6 seconds within the 44444 data records for user class 2 on that particular link in both cases the 6 seconds is simply added to the minimum generalized cost for that link as used within the assignment Therefore in both cases the extra time may influence their route choice However in practical terms it is much simpler to set a single parameter under amp PARAM than to include explicit penalties for every link which requires it Although on the other hand explicit penalties under 44444 can be made much more precise A possible modelling disadvantage of assigning a fi
8. The default is TRUE and it needs to be stressed again the alternative should be used with great caution In particular it is not recommended to use with KINKY F with simulation networks In addition if KINKY F then care should be exercised that parameters that control the power of cost flow curves such BCRP or PMAX should be less than or equal to 5 0 15 89 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 39 15 39 1 15 39 2 5120257 Apr 15 Section 15 In general KINKY F should only be used in research based applications and even then for very specific purposes For example it may be useful in studies of system optimal assignment and system optimal tolls see 7 11 9 Note that KINKY applies to all cost flow curves i e both buffer as input and simulation as calculated Bus only Lanes Bus only lanes in SATURN represent extra lanes along simulation links which are for the exclusive use of public transport vehicles as coded under the 66666 network data records 6 9 The format specification for identifying bus lanes and whether they are nearside or offside are given in Section 6 4 9 2 Flows in bus lanes Bus flows on a link are assigned to a bus lane and are therefore removed from normal traffic but only if certain criteria based on the next link in the route are satisfied Two sets of acceptance criteria are applied the first is fairly obvious but may be overly
9. so that we may distinguish cost from its sub components such as time and distance A minimum cost matrix is the complete matrix of O D minimum costs as extracted from the tree Skimming Trees To skim a tree is to sum a particular quantity e g time distance toll etc etc link by link along the minimum cost paths for each O D pair For example we may wish to calculate the distance along the O D path which minimises cost Therefore we distinguish between the quantity which is used to build the tree and the quantity which is skimmed Skimming is very often an essential step in scheme evaluation Within SATURN skimmed O D matrices may be obtained in two different ways via trees as described here or much more usefully via forests as described in 15 27 3 Trees may be skimmed to produce skimmed matrices as part of the tree building option 14 within SATLOOK thus the ij th element in the output matrix is e g the distance from origin i to destination j as summed along the links in the minimum cost time path from to j Note that using a tree to produce say distance skims does not necessarily accurately reflect the average assigned distance for trips between a given O D pair in those cases where several different routes with several different distances are used within the assignment process Skimming a tree only gives one particular route distance and indeed other routes may give lower or hi
10. 15 167 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 56 6 10 00 60 5120257 Apr 15 Section 15 Eliminating zero flow links can substantially reduce CPU time in all instances since empirically it appears that over 50 of aggregate spider links may be unused N B In principle it is possible to apply the same rules to basic networks but since in practice there are very few if any proper links with zero flow then it is not worth the added effort Results from Representative Networks Pure Assignment SATASS only We display below a table of results from a randomly selected set of real life networks in which we give The number of zones and user classes which are the same for both basic and aggregated networks The number of assignment network nodes and links in the base network The number of nodes and links in the aggregated network The number of newly created aggregate links which are duplicates joining the same A and B nodes The total number of equivalent base links which the aggregate links map into The ratio of base aggregate CPU time for a single Frank Wolfe assignment i e NO SATSIM 15 168 SATURN MANUAL V11 3 i SATURN Special Options and Facilities Table 15 2 Performance Comparison SATASS CPU time only Aggregate Original Network Network Network Zones New Town 1 5 Duplicates Equivalent Nodes Links Nodes
11. Eco oi browse Double click to run this command again LP amp VDU files in model folder Show MADR CC Quiet Quick ATKINS This will load up the SATSTAT module requesting the network s that you wish to extract the summary statistics from p SATURN Launch P Don 9 Ss r el a Home Matrix Operations Post Assignment Viewers Conversion Advanced Versions Experimental Tools Support ene T Ga S 339 P3 P1X ol MXM1 E Gus d SATCH MC GSATLOOK MC SATOFF o MM io o S P1XDUMP 1 SATUFO MC p X SATURN SATNET PMAKE SATALL SATSIM SATSTAT en i S SATSTAT gt 6 j B C Users SWAI2000 AppData Local Atkins SATWIN SATSTAT Module EQ Go Browse Model Default Test Model SATURN version 11 3 Task Description Module Parameters Executed Model F UOIJRUUOJUT daH maA a Network File 3 x Network File 4 x Extra Command Line Parameters Free Text Parameters Tarer IS CL LP amp VDU files in model folder akokr ATKINS Quiet Quick The two networks we wish to compare are Reference Case EPSOM98AXX UFS and Development scenario EPSOM98RXX UFS We now select both these networks to run through SATSTAT as shown below Note that in this example we have changed the Working Folder to C Users SWAI2000 AppData Local Atkins SATWIN but the files may be located in any folder 512025
12. If the bitmap display is too intense it may make the over printed P1X displays difficult to see This may be corrected by reducing the intensity of the background by setting a scaling factor between 0 and 1 set within Display Background or via the xyb file 15 43 1 the lower the factor the whiter the bitmap The default scaling factor is 1 0 but may be changed globally via the namelist parameter SCABMP in the P1X preferences file p1x0 dat This option may be particularly useful within PMIAKE when a new network is being traced on a bitmap image Maximum Bitmap File Sizes The size of a bitmap file which can be read by P1X i e the number of pixels in both the horizontal and vertical dimensions is limited to certain upper limits e g 2003 x 2004 This may create problems for users since it is quite easy to create omp files with an almost infinite number of pixels depending on the geographical size of the file i e the number of square kilometres and its resolution Some compromises may be necessary within SATURN For example if the omp file covers an area of 1 km x 1 km with 2 000 pixels in each dimension then one pixel in the omp file covers 0 5 metres which for most purposes should provide sufficient resolution However if the user windows in to a 20 x 20 metre display in order to look at a single junction then each pixel in the Original omp file covers 0 5 20 equals 1 40 th of the screen and the
13. hence double counting the effects of queuing But if UNIQUE is set to T within the amp PARAM of the dat file the extra delay is imposed at only one of the links that with the minimum capacity which therefore represents the true bottleneck This option is useful if say an existing buffer link A C is split by a mid link node B with no other changes and the same link properties apply on both A B and B C SATURN Summary Statistics Reporting Tool SATSTAT SATSTAT is a tool used to automatically extract and summarise convergence and summary performance statistics for each network s into a CSV file The resulting CSV files may be then be readily imported into the associated MS Excel spreadsheet and comparisons undertaken between different networks SATSTAT consists of two parts i a Fortran 32 bit program to extract the Summary statistics and li an MS Excel spreadsheet to undertake the comparisons SATSTAT FORTRAN Program For each UFS network s selected the SATSTAT Fortran Program v3 00 will Automatically extract SATURN convergence assignment simulation statistics and queues using the standard reports available through SATLOOK SATDB P1X etc Produces summary outputs in MS Excel CSV format of Model Convergence NITA NITS flows gaps epsilon SATLOOK option 8 Model Runtimes SATNET Assignment Simulation SATLOOK option 8 Matrix Totals including Origins amp Destinations within Buf
14. hooked movement Right turning vehicles at traffic signals i e turns coded as X have priority over left turning vehicles coming from the opposite direction The values allowed for NOTUK are 0O neither assumption the default UK value 1 assumption i only as in Australia apart from Victoria 2 assumption ii only 3 both i and ii as for Victoria and New Zealand The traditional i e dating back to the 1970 s default value in SATURN is 0 implying that opposing right turns in the UK do hook and therefore interfere with one another However in the 21 Century UK the opposite is almost certainly the norm and paradoxically a value of NOTUK 1 would be recommended However setting NOTUK 1 on existing networks may not be a good idea if a large number of individual turns have been given a Priority Modifier D which reverses the definition of hooked not hooked see 6 4 2 7 l e if you set NOTUK 1 but do not change XD to X then all those turns will be assumed to hook Right hand Drive LEFTDR F Although clearly designed for British conditions with drive on the left it is equally easy to use SATURN for drive on the right To invoke drive on the right set the parameter LEFTDR to FALSE either universally by default in SAT1O0KEY DAT Appendix Y or network specific 6 3 1 Differences occur in the input in that simulation links need to be input in strictly counter clockwise order for ri
15. or pcx format as opposed to e g jog gif etc formats although jpg is allowed as output see 11 3 6 However other graphical formats may almost certainly be converted into a omp format by making use of standard software such as Paint Where or how the bitmap file is obtained is not strictly relevant it might be downloaded from e g OS sources scanned from a road map dumped from a GIS software package or even output from a different run of P1X for a different network The important thing is that it be in omp format and equally important that the area which it covers be identifiable Thus in order for P1X to draw a bitmap background within the windowed area covered by a network plot it is necessary to know a the precise area covered by the network window and b the full area covered by the omp file in effect the co ordinates of its 4 corners so that the degree of overlap between the two may be ascertained This may not sound too difficult indeed most of the time it isn t the tricky thing is being able to obtain the co ordinates of the bitmap and of the network within the same reference system Note that it is the network window which controls the region plotted and that the bitmap must be manipulated to fit onto the area chosen by the P1X network window rather than the other way around Thus for every omp file used by P1X say picture bmp it is necessary to set up a further very small file
16. typical DfT parameters defined above Thus link 6 7 has a length of 90 metres but a capacity of 1400 a free flow speed of 63 kph etc as taken from the previous D record for capacity index 4 0 oot oaojuwh WD FE PRPREPWAWAKROORPRP UU OINAWARONTWOWANO D D D D D D D D D D D D D Further Notes 1 The D records can appear anywhere within the 33333 records and can be applied to buffer links that precede them 2 By default see note 4 below the five required input data fields free flow speed speed at capacity capacity the power n and capacity index must appear within the same fixed columns as normal buffer links e g the free flow speed in columns 11 15 But N B note that the required columns differ under DUTCH T see 15 20 3 Note that unlike standard buffer records where either speeds or times may be used the default speed flow curves are only based on speeds It is assumed therefore that buffer records which make use of speed flow curves have an S in column 29 89 under DUTCH T 4 Problems associated with fixed columns and differences between DUTCH T or F may be eliminated by setting a parameter DCSV T under amp PARAM in the network dat file in which case the 5 necessary fields may appear in free format following the D in column 1 l e they must appear in the correct order and be separated by either soaces and or commas 15 26 SATURN MANUAL V1 1 3
17. 54 4 0 2239 5 17 51 5 0 1 27 2 245 599 2 6 577 8 0 8 42 9 0 52 49 6 118 8 301 8 158 2 2887 2 15 131 5120257 Apr 15 Section 15 not found ISE 3 3 1 3 156 68 397 0 483 5 88 1 6292 9 0 1 lt gt 0 100 2 65 3 O 1519 2 345 2 217 9 0 1629 9 2647 6 54 4 0 2239 5 17 51 5 0 1 27 2 245 599 2 6 577 8 0 8 42 9 0 52 49 8 118 8 301 8 158 2 2887 2 not found 156 9 3 1 156 6 397 0 483 5 88 1 6292 9 0 1 lt gt 0 100 2 65 3 O 1519 2 ase 217 ou 0 1629 9 2047 6 54 4 0 2239 5 17 651 5 0 1 27 2 245 599 2 6 577 8 0 8 42 9 0 52 49 8 118 8 301 8 158 2 2887 2 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 49 2 7 SATURN Versions 15 50 15 50 1 15 50 2 5120257 Apr 15 Section 15 SATSTAT will work for all versions of SATURN v10 available i e v10 1 through to 10 9 It should operate correctly on any UFS files created under these various versions as well as undertaking the summary reporting using any of these versions SATMECC Marginal Economic Consumer Costs Basic Theory The principle of marginal cost was introduced in Section 7 11 9 where equation 7 46 defined the marginal cost for a separable cost flow curve i e one where the cost of travel on link a is a function only of
18. Clearly the same technique may be applied in both directions when both links A B and B C are two way assuming that U turns are banned at B hence an aggregate link A C replaces A B and B C while C A replaces C B and B A The same technique may clearly be extended to the case where there are a series of more than one two arm nodes between A and B such that a single link from the start to the exit node replaces all the intermediate links and all the intermediate nodes are removed This form of configuration occurs not infrequently in SATURN networks when a number of artificial nodes are inserted between two main nodes in order to give the link shape although clearly a better method is to define the shape via a GIS file In fact a common theme in network aggregation is that the degree of potential aggregation and time savings that are available may depend very sensitively on the coding techniques adopted 15 56 2 2 Aggregating Multiple arm Nodes 5120257 Apr 15 Section 15 It is also possible to eliminate nodes with more than 2 arms for example a 3 arm node N as illustrated below A B May be aggregated into a triangle 15 159 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 Such that the cost on the aggregate link A C is the sum of the original costs on A N plus N C Note that it is not necessary to create a U turn link say from A to A equivale
19. Highway Assignment AM Peak Highway Assignment i Inter Peak Highway Assignment i r PM Peak i Not used Ly H 7 z E H k H A i H E z i H F a a H m 4 F d H d E t e 5 z T ka E kJ wake Not used by SATURN Figure 15 7 Advantages of Multi Core Processors Highway Assig nment AM Peak Not used by SATURN 15 52 1 Additional Programs Parallel runs can be performed with the aid of two programs MONITOR and WAIT 5120257 Apr 15 15 139 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 135 92 1 1 Monitor MONITOR takes a snapshot of all running processes in Windows at regular user specified intervals and checks if a user specified program is still running The program terminates when the user specified program is not one of the currently running processes MONITOR takes two parameters Parameter 1 the SATURN program to run in parallel eg SATALL EXE Parameter 2 the time interval in seconds for taking snapshots of running processes to determine if the SATURN program specified by parameter 1 is still running eg 10 15 52 1 2 Wait 15 52 2 5120257 Apr 15 Section 15 WAIT used within a batch file causes the batch file to pause where it is called for a user specified number of seconds b
20. SATURN Special Options and Facilities 15 9 6 15 10 15 10 1 5120257 Apr 15 Section 15 3 It is quite possible that users would wish to set up curves with characteristics identical except for the link capacity to represent say dual 2 and dual 3 roads with identical speeds in which case distinct capacity indices should be used for different lanes The requirement for link rather than lane capacities should be noted 4 D records are good candidates for inclusion under INCLUDE see 15 30 such that a standard set of default soeed flow curves may be recorded in a single file and applied to a wide range of networks 5 Default speed flow curves may also be applied to simulation links where record 2B see 6 4 1 excludes any time speed and capacity data but refers instead to a capacity index which as with buffer links defines the link speed flow curve Default Speed Flow Curves COBA 10 Formats An option added in release 10 7 permits default speed flow curves to be defined directly in terms of COBA 10 speeds and flows such that the best fit value of the power n is calculated by SATNET rather than being input directly by the user To invoke this option the default soeed flow records must be altered as follows a Write COBA in cols 36 40 in place of N 46 50 under DUTCH T b Write the speed at the breakpoint S in cols 46 50 56 60 under DUTCH T c Write the breakpoint flow F in cols 51 55 61 65 u
21. There are a variety of circumstances under which the simple add a pcu simulation method may give unreliable results where unreliable generally means extremely high absolute values Therefore a number of alternatives have been included within SATMECC as follows 15 134 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 If the turn is over capacity in the base simulation we do not have to perform a second simulation to calculate MECC since the main impact of an extra ocu on an over capacity link is essentially to make the queue on that arm one pcu longer rather than changing the flows through the node Thus we may combine equations 7 46 and 8 5b or 8 116 in the case of shared lanes to obtain Equation 15 18 MECC LTP 2 V C lf the turn is almost at capacity strictly 90 lt V C lt 100 then a negative increment of 1 pcu is used in the first instance rather than an increase of 1 0 But see point 7 below If the turn has zero or very low flow arbitrarily under 5 pcu hr the turn is simulated at flows of say 5 0 and 6 0 pcus hr as opposed to say 0 0 and 1 0 pcus hr since very often there can be very highly significant changes between no flow and a very small flow This is particularly true of X turns at signals even more so when they come from a single lane with other shared movements If the addition of 1 pcu takes a turn beyond capacity then t
22. capacity speed time capacity and power but include the distance and capacity index The program then substitutes the default speeds etc for the missing records In fact it is not even necessary to code the distance if the SHANDY option is in effect see 15 10 N B It is necessary to leave all four of the above entry fields blank zero if one of them is included then it assumed that the other entries of zero are all valid entries and the default option is not applied 15 25 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 Thus all links with the same capacity index will have an identical speed flow curve plus capacity Note that the actual times need not be identical since these will depend as well on the distance which is coded separately for each link One advantage of this option is that you can make universal changes to the speed flow parameters for a set of links by simply changing a single record rather than several The option should also be extremely useful for networks which are defined by graphical input in some form here link distances can be calculated from node co ordinates so that the only input information required from the user apart from whether a link is one way or two way is an index which determines the remaining parameters An example of an input data file using these conventions is illustrated below where default indices 1 to 14 are equivalent to the
23. destination j demand segment user class c time period t and mode m The convergence profile of GAP SD over cobweb loops is similar to the assignment profile of GAP over internal loops i e decreasing rates of improvement as convergence improves as shown below in Figure 15 12 The objective of CASSINI is therefore to minimise the overall CPU time required in order to achieve a satisfactory degree of convergence within both SATURN the supply model and the supply demand model i e both GAP and GAP SD must be sufficiently near zero at the end of the process We assume here that the CPU time required to run the demand model on its own i e to produce the new set of trip matrices is effectively fixed per loop and that internal convergence within the pure demand model is not an issue CPU may be reduced by either reducing the time per SATURN run and or by reducing the total number of cobweb loops or as it turns out by reducing the former and not increasing the latter too much We achieve this by noting that it is not efficient to spend a lot of CPU obtaining a highly internally convergent SATURN assignment for a particular trip matrix if that trip matrix is then going to be considerably changed by the next supply demand loop For example there is no point in having link flows accurate to 0 1 if trip matrix cells are varying by 10 We therefore apply a principle of relaxed convergence see 7 4 5 3 by specifying relativ
24. enter Z in columns 2 5 with a C in column 1 and A in columns 6 10 Reverse the two fields for an inbound centroid connector Note that post 11 1 the requirement to identify zones by a C in an appropriate column may be relaxed by the use of NO333C T whereby any input node number which is less than or equal MAXZN is assumed to be a zone whether or not a C has been included This should make it easier to create KNOB files using external packages but clearly may create problems if zone and node numbers overlap Centroid connectors to from internal simulation links are more complicated and users are advised to consider using Wildcard entries as described below which only require the zone name plus C in an appropriate field Otherwise to define an outbound centroid connector from Z to link A B enter C Z in columns 1 5 A in columns 6 10 and B in columns 11 15 For an inbound centroid connector from A B to Z enter A in columns 1 5 B in columns 6 10 and C Z in columns 11 15 Post 10 9 5 the above rule has been relaxed so that an outbound centroid connector from zone Z to link A B may be defined by entering Z in columns 1 5 and B only in columns 6 10 This after all is how the centroid connector appears on the network plots a dashed line from Z to B If there is then only one possible link A B which is so connected the value of A is inferred However if there are multiple centroid connectors between Z and B the method fails Similar
25. hence one environment variable is required as in 2 STARTE on ORNS INEU oo TNE Ui 4 Starts the first SATURN run WAIT 5 15 140 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 53 5120257 Apr 15 Section 15 5 Waits for 5 second to avoid simultaneous access to SAT1OKEY DAT START SATURN INPUT2 INPUT2 6 starts the second SATURN run START W MONIC SATA 1010 7 starts monitoring SATALL EXE every 10 seconds and MONITOR terminates if SATALL EXE is not found in the latest snapshot of running processes controlled by the Windows Operating System 8 SATURN MULTI CORE applications are multi threaded versions of existing programs that are able to take advantage of the additional processors either in the form of physical cores or virtual threads available on most Intel AMD powered standard desktop PCs The start command will open a new command shell to run SATURN every time it runs If the user wishes each command shell to be closed at the end of the operation create a copy of the existing SATURN BAT and add an extra line at the end saying EXIT So for example if the amended batch file was called SATURNEXIT BAT the revised command line would be SANE SvEIMULINI OC IE IE INPUT Zs sy LINE UME 225 SATURN Multi Core Applications SATURN MULTI CORE applications are multi threaded versions of existing programs that are able to take advantage of the additional processors either i
26. pcu hrs lt Proportion carried over gt Total Travel Times Total pcu hrs lt Proportion carried over gt Travel Distance Total pcu kms lt Proportion carried over gt Average Speed fOverall kmh lt Ratio gt allele lalla oO Delay Total pcu hrs Delay Vehicle mins veh Congestion Index mins veh km Average Trip Length km Simulation Queues pcu h Ave Queue DA1433 Queue at End DA1463 Turn Penalties pcu hrs hy not found not found Turn Penalties number not found not found Belek ee le ele fe fel el le oa oO _ k fe on MN N _ M ica FB9 Eile Edit View Insert Format Tools Data Window Help ae ee 7 dh Ga 5048181 SATURN Support IJWright Atkins Date Created 15 03 07 Import CSY Version 3 00 11 Convergence Summary for EPSOMSBAXK EPSOMSSRXX EPSOMSSRxXX EPSOMSSRXX Loops N 12 a 11 11 Flows 94 5 98 1 96 1 96 1 GAP 0 302 0 333 0 333 0 333 Statistics Summary Results EPSOM98AXX STA EPSOMG8RXX STA EPSOMSBRXX STA EPSOMSSRXX STA Matrix totals pcus hr S013 Transient Queues Total pcus lt Proportion carried over gt Over Capacity Queues pcus lt Proportion carried over gt Link Cruise Times Total pcu hrs lt Proportion carried o
27. reduced flows downstream of V gt C movements is correctly retained as is the distinction between demand and actual flows on all intermediate band links Equally any blocking back effects are retained under FCF in that the capacities C used in equation 8 5 are the capacities post blocking back However any reductions due to blocking back are fixed and will not change as a result of any flow re assignment within the intermediate band On the other hand a lot of the detailed information that is provided by the normal simulation for example the saw tooth style queue profiles at signals lane choice blocking back factors etc etc are either no longer available or else retain their values input at the point of fixing Equally the most essential information which is being passed from the simulation to the assignment the flow delay curves Is by definition fixed rather than variable by loop For this reason FCF networks should only be set up once a reasonably stable set of cost flow curves have been obtained i e that the simulation assignment convergence is good Creating a FCF Network using SATCH The first step in creating a master FCF network is to use the standard network cordoning program SATCH to add FCF nodes to an existing well converged network old_base ufs e g SATCH old base control To do so a new logical control parameter DOFCF is set to TRUE within amp PARAM in control dat All o
28. single core reduces wastage it is not a substitute for having additional physical cores instead There are various different propriety names for this technology Intels Hyper Threading HT technology available on most of their medium and high end processors is probably the most widely known Intel HT uses this principle whereby each physical core is able to run two threads simultaneously As far as SATURN Multi core applications are concerned its applications will automatically generate N threads either up to the maximum available as defined by the operating system the user defined MCNUM parameter or the maximum number of threads that the application may be broken down into as defined in the batch files so that tasks may be undertaken simultaneously The Windows Operating System takes the threads generated by the SATURN application s and schedules them to run on the threads available No further user intervention is required Performance Gains The performance gains available are dependent on a large number of variables namely PC hardware including the processor operating system and RAM available and Model size and configuration particularly with the number of zones and user classes The performance testing across a range of different sized SATURN models demonstrated the significant reductions in model runtimes available with SATURN Multi Core In the following paragraphs examples are provided for a medium sized model o
29. stochastic routes in order to assess qualitatively the effect of different parameter values In order to do 1 it is essential to have invoked the SAVEIT option during the assignment see Section 15 23 and to then select the desired iteration number or numbers As long as SUET KORN and KOB are identical to those values used during the assignment then the routes SHOULD be identical But N B this reproducibility is a function of how your program has been compiled vis a vis random numbers since there is a choice between using your own machine dependent random number generating functions which are probably NOT reproducible and using a SATURN supplied function which is If your programs were supplied as executables from Leeds or Atkins worry not if they are home compiled check Method 2 may be used for example to see how large a value SUET can take before the routes generated using say minimum time as the basis become unrealistic Trees Forests and Arboreta A tree refers to the set of shortest routes from one origin to one or all nodes zones in a network As such a separate tree is calculated on each iteration within an assignment A forest is therefore an aggregation of all the trees from a single origin over all internal assignment iterations weighted by the fraction of the trip matrix as ultimately assigned to each iteration More precisely the forest value for a link is the proportion of trips from
30. the two origins paying tolls in slightly different proportions rather than the extreme all or nothing case where one origin pays tolls and a second does not Note 7 in 15 27 6 discusses this issue further 15 66 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 27 4 5120257 Apr 15 Section 15 Minimum Cost Matrices vrs Skimmed Average Cost Matrices In effect minimum cost matrices the matrix of minimum possible costs from O to D 15 27 1 are a particular example of matrices skimmed from a single tree whereby the quantity which is skimmed Summed is the same quantity which defined the minimum cost paths However since the minimum O D travel costs are obtained as an integral part of the tree building process it is not necessary to do a subsequent skim which would clearly give identical results However it is also possible to construct a matrix of costs by skimming a forest where in this case the cost refers to the generalised cost used in the assignment process see 7 11 1 which in turn are the same costs upon which the forest of assigned O D routes are based In this case the skimmed cost will be the weighted average cost over all O D routes used We recall that Wardrop s Principle requires that at equilibrium all used routes have equal and minimum costs so that in the case of perfect equilibrium the minimum cost matrix will be identical to the cost matrix obtained
31. unobtainable would this problem would not arise The Batch Procedure SIGOPT A new batch procedure SIGOPT BAT has been introduced in Release 10 8 16 to optimise stage times and or offsets in a ufs file and to create a new output file s It effectively supersedes both P1X in terms of stage times and SATOFF in terms of offsets Output files may be either a UFS b DAT and or c RGS SIGOPT makes use of existing routines within P1X but runs in a non graphical non interactive mode such that it resembles any other batch mode program It is called via SEGOPT net KR Control KP si ldat where control dat optional is an ascii file which sets various options filenames etc via Namelist and may also contain a list of selected nodes for optimisation The full list of parameters with their defaults is listed below Fildat optional specifies the name of an output dat file containing the revised network dat file Fildat may equally be specified as a Namelist parameter within control dat Note that if the input network file net dat references INCLUDE files within the 11111 records then the output file fildat copies these files directly into the new 15 82 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 31 7 15 31 8 5120257 Apr 15 Section 15 11111 records the INCLUDE files may be recreated and potentially renamed using text editing cut n paste See 11 9 2 1 The filenames fo
32. 1 5 Determining Fuel Consumption Fuel consumption is an area of major concern to traffic engineers for obvious reasons It is also an area which as with emissions 15 33 is probably best handled post processing i e users will have their own particular favourite model or formulae for fuel consumption which will require both data from SATURN such as flows and or speeds and exogenous data such as graphs of fuel consumption vrs speed In such cases the best option is to dump the required SATURN data into say a link based text file using SATDB and to pass that data into their own procedures Or it may also be feasible for users to set up their own equations calculations using the data manipulation facilities within SATDB 11 10 8 1 However there are also internal fuel consumption models within SATURN Thus in order to estimate the total amount of petrol consumed within the simulated network SATURN uses the following equation f FLPK d FLPH t FLPPS s FLPSS s where f fuel consumption in litres d total travel distance in vehicle kilometres t total delayed idling vehicle hours S total number of primary or full stops at an intersection e g where a vehicle arrives at the end of a queue So total number of secondary stops e g stop starts while a vehicle moves up in a queue and the weighting parameters FLPK etc have been assigned default values as follows FLPK 0 07 FLP
33. 23 GAP 0 302 26 2 Statistics Summary Results FRPSOMEGAA K STA 2A 30 Matrix totals pcus hr 5013 1 44 Transient Queues Total pcus Seles 47 lt Proportion carried over gt 0 5 53 OverCapachky Queues pcus 1 4 56 lt Froportion carried over gt 0 0 6S Link Cruse Times Total peu Ars Ale 66 Froportion carried over gt 0 1 Fa Total Travel Times Total pou hrs 158 4 76 Proportion carried over gt 0 2 63 Travel Distance Total peu kras Saan 56 lt Proportion carried over gt 0 1 93 Average Sheed Overall Krahl J3 56 Ratio I2 Ao 105 Delay Total pou hrs 40 9 107 Delay Vehicle mins veh 0 45 108 Congestion Index mins veh km Tar 109 Average Trip Length km 04 111 Simulation Queues pcu h 6114 Ave Queue 041433 IE 115 Queue at End DA14863 5 40 122 Tum Penalties pcu hrs hrl not found 129 Tum Penalties number not found 15 49 2 4 Summary Reports i 0 SATURN ap scp 2E FE Ee Import CoV At the highest level the summary reports are available for Convergence in the Assignment Simulation loop Number of loops undertaken Flows achieved GAP achieved Summary Statistics post simulation for TOTAL flows Matrix totals excluding intra zonals 15 128 5120257 Apr 15 Section 15 EPSOMGGR AA
34. 31 2 5120257 Apr 15 Section 15 On the other hand some reaction of signals to altered flow is clearly necessary Perhaps a good compromise for future year networks is to first set signals using engineering judgement carry out one full assignment followed by a stage time optimisation and one more assignment where by assignment in this case we refer to a full run of SATURN with assignment simulation loops internally If the improvements in total network travel time are significant this procedure could be repeated always bearing in mind the possibility of producing unrealistic flow and green time patterns and even deterioration of overall travel times There is another possible need for a fully automated approach this is the case where a network is not yet in existence and initial green times can be determined to impose a preferred flow pattern on traffic The traffic engineer then has the freedom to pursue the iterative loop until the signal settings are found that lead to the lowest network travel times Optimum Stage Times using PIX In order to optimize stage green times a special option has been included within the P1X Network Editing options see 11 9 13 to automatically consider all signalised junctions and to optimise all green times using options as detailed below This option is to be found within Global Operations on Signals and would normally be followed by the creation of a new UF file and or dat file containi
35. 5120257 Apr 15 Section 15 The methods by which the required entry exit flows are monitored with an assignment differ depending on whether not Network Aggregation 15 56 is invoked or not SPIDER T or F Thus if Network Aggregation is not invoked SPIDER F the 4 demand entry exit flows which make up the weaving segment two possible entries and two possible exits are continually monitored while the assignment is taking place and at the end of the assignment and prior to the next simulation that information is used to calculate the reduction factor as described above Strictly soeaking only a single flow is monitored since the other 3 flows may all be obtained knowing the total demand flows on the entry exit arms On the other hand if SPIDER T and if all the nodes within the weaving segment e g nodes 10 to 20 inclusive in Fig 15 5 are aggregated then all the possible weaving movements 1 3 1 4 2 3 and 2 4 will either be distinct aggregated links or part of larger aggregated links In either case the necessary flows may all be taken directly from aggregated link flows and no extra steps are required during the assignment itself The method is therefore much more efficient and significantly faster in terms of CPU For additional discussion on aggregated networks see 15 56 7 4 Simulation Capacities Within the simulation the reduction factor is applied to the saturation flows for all turns out of the motorway links
36. 98 1 96 1 98 1 SEA Sii 0 02 0 02 0 333 EEE a co NN NMN MR S O ho O o PCNEAR gt 5 5 M 6 Statistics Summary Results EPSOM9BAXX STA EPSOMG8RXX STA EPSOM9IBRXX STA EPSOMO8BRXX_ STA Matrix totals pcus hr 5013 1 5170 5170 5170 Transient Queues Total pcus 25 196 3 196 3 196 3 lt Proportion carried over gt 0 5 3 0 3 0 Over Capacity Queues pcus 1 4 89 5 a915 lt This Time period gt 1 4 61 6 61 6 lt Next Time period gt 0 Pan ei lt Proportion carried over gt 0 0 8 6 5 6 5120257 Apr 15 15 129 Section 15 SATURN MANUAL V11 3 SATURN Special Options and Facilities 15 49 2 5 Importing Additional Networks This may be repeated for any number of networks If further reporting columns are required an existing column may be copied across as shown below EXISTING EJ Microsoft Excel Summary Report v3 00 xIs Format Tools Data Window Help Sa F 5048181 SATURN Support IJWright Atkins Date Created 15 03 07 Import CSY Version 3 00 Convergence Summary for EPSOMSBAXX EPSOMSSRxXX Loops N 12 11 F lows 94 5 98 1 GAP 0 302 0 333 CICI Statistics Summary Results EPSOM98BAXX STA EPSOMO8RXX STA Matrix totals pcus hr Sots 5170 Transient Queues Total pcus 196 3 lt Proportion carried over gt p 3 0 Over Capacity Queues pcus lt Proportion carried over gt Link Cruise Times Total
37. CO ORDINATES SEE 6 8 Cols 1 A C if columns 2 to 10 contain a zone number Cols 2 10 The node or zone number Cols 11 15 Its X co ordinate Cols 16 20 Its Y co ordinate A4 BUS ROUTES SEE 6 9 Cols 2 5 The name of the route which must be numeric Cols 6 T if the route is two way and the node order is exactly reversed in which case the reverse route need not be coded otherwise leave blank Cols 7 10 The route frequency in buses per hour Cols 11 15 The number of nodes through which the route passes i e the number of node entries following Cols 16 25 The first node on the route Cols 26 35 The second node on the route etc up to 6 nodes column 75 15 21 15 21 1 5120257 Apr 15 Section 15 If the route passes through more than 6 nodes the list of nodes is continued on a second or even third record starting in cols 16 25 N B The strict column formats do not apply if EZBUS T independent of the value of DUTCH A5 LINK AND OR TURN COUNTS SEE 6 10 Identical changes to A2 above B SATPIJA SEE SECTION 13 2 1 Link and or turn counts are specified as under A 5 and A 2 above Essentially the changes are made anywhere that it is possible that 8 digit buffer node numbers MIGHT be input but NOT in those areas where only simulation node numbers may be used Referencing Data Arrays Via Dirck Access Codes General Principles Certain programs notably SATDB and P
38. Dirck Van Vliet Transportation Research Vol 12 7 20 1978 and reproduced in Appendix T Other algorithms may have slightly different functional forms but all share the same basic property of being increasing functions of the number of nodes and the number of links in the network Similarly the cpu time required to load a single origin row of the trip matrix is proportional to the number of destinations times the number of links Thus the total time required to carry out a single all or nothing assignment step the basic building block of the Frank Wolfe algorithm is an increasing function of a the number of origin zones b the number of nodes and c the number of links Any reductions in one or all of these should therefore lead to reduced cpu times network aggregation achieves this by reducing the number of nodes and or links 15 158 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 56 2 In addition network aggregation reduces the cpu time involved in building trees during post assignment analysis such as skimming select link analysis etc etc See Section 15 56 7 A condensed version of the material that follows was presented at the ETC European Transport Conference in Glasgow 2010 by Wright et al and reproduced in Appendix S pdf version only Aggregation Techniques 15 56 2 1 2 arm Links in Series The simplest example of combining two links in series into one has been illustrated above
39. Equilibrium solution will almost certainly be somewhere between the two values Method a is therefore recommended unless one is specifically interested in the average O D costs When skimming from a forest under the standard Frank Wolfe method of assignment as opposed to path based or OBA the level of convergence achieved by the extra SAVEIT assignment if one is required becomes an issue 15 23 2 Thus the routes generated by a SAVEIT Forest will not in 15 69 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 general reproduce the same routes and the same link flows as generated by the assignment proper they are only an approximation The differences are reduced by better convergence i e increased values of NITA_S which leads to more accurate skims but it also means more cpu time Compromises may be required N B These problems do not arise if the skimmed forests are based on the actual assignment routes as opposed to an extra SAVEIT assignment e g if UFC109 T see 15 23 3 1 Since the precise route flows generated under Wardrop Equilibrium are not unique see 7 1 6 and 15 23 8 neither are the average forest weighted O D times distances etc cost components which are skimmed from them even if convergence were perfect In addition the average OD speed matrix obtained by dividing average distance by average time would not be unique either This may have implications fo
40. Links 3 022 2 858 362 2320 3026 ata s ss O1 1 964 24 232 3 2 s 1 246 16 379 6 440 1 063 6 198 949 20 116 1693 21 229 4 187 19 947 3 444 26 602 112 63 596 14 422 92 2 4 926 53 363 17 028 109 568 9 992 68 584 5 601 60 325 6 064 61 922 22 645 London 93 905 8 833 96 296 23 593 LoHAM 5 624 185 576 21 348 151 776 13 513 The networks are arranged in order of increasing number of zones 4 263 gt Oo 5 89 3 758 50 401 3 204 175 665 13 374 200 797 13 5 set e00 GMTU 993 East ii Central M South 2 520 CO N 13 515 177 59 567 896 387 600 65 183 s 42 665 30 633 75 178 556 742 28 587 335 510 57 877 153 240 119 534 962 301 3 75 It is difficult to draw any universal conclusions from the above table clearly the improvement in CPU time is a function of certain network coding idiosyncrasies e g whether or not stub zone connectors are widely used There is a tendency for networks with smaller number of zones to be more efficient under aggregation as we might expect since the more zones there are the more opportunities there are to reduce tree building times compared to the overheads involved in constructing aggregate link costs 15 56 6 2 Full Assignments Assignment amp Simulation Since SATURN incorporates both assignment and simulation sub models and the CPU time for the simulation is unaffected by network ag
41. NUSKIM T in the preferences file SATLOOKO DAT The default is provisionally T Alternatively the preferences option may be invoked in the command line to define an alternative local preferences file rather than over writing the master version For example SKIM ALL net mat PREF mylookO dat Substitutes the preferences file mylookO dat which should be in the same folder as net ufs etc 15 28 Variable Program Dimensions SATURN is available in differently compiled exe files each allowing for a different maximum problem size The smallest standard array size is version B with intermediate versions available up to the largest X7 further details are listed below Array Level Simulation Junctions Assignment Links 900 7 900 1 000 22 500 1 500 32 500 20 O ew rw 80 O ew ow O w O ow nw w O ow ew wo 5120257 Apr 15 15 74 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities Array Level Simulation Junctions Assignment Links Zones 4 000 93 500 2 000 4 900 103 500 2 000 5000 112 500 2 000 2000 The above table provides a quick reference guide to the principle variations between the different licence levels but other constraints such as the number of simulation links or turns will also determine the licence level required to run specific models Beyond Level K the number of zones available is capped at 2000 to reduce excessive memory requi
42. Options and Facilities class to separate threads and therefore is most efficient if the number of threads available equals the number of user classes 15 53 1 Programs Available SATALL was the first program to be modified to function with multiple parallel processors and was first released with version 10 8 22 Since then further development work has been undertaken to expand the number of programs available with multi threaded capability as detailed below The development work was completed with the release of 11 2 05 in March 2013 Program Status How to Access Version Comment The assignment routines are Replacement l SATALL Final SATALL EXE and v10 8 22 multi threaded internally Release onwards whereas the simulation set MULTIC T l remains unchanged Final Replacement v10 9 22 Various skimming options may SATLOOK Release SATLOOK EXE and ee ae be run using multiple threads set MULTIC T in parallel See 15 53 3 2 Replacement Generation of UFO from SATUFO EXE and existing UFC undertaken SATUFO Beta set MULTIC T v11 1 02 using multiple threads in Release and or embedded onwards parallel Replaces previous within SATALL EXE distributed SATUFO_MC if SAVUFO T process Undertaken using a distributed version whereby the PIJA process is split by blocks of origins and multiple New versions of SATPIJA run for Final SATPIJA_MC BAT v10 9 22 each A final SATPIJA run Release and onwards combines the individu
43. PCU kms by user class 3 produced per sector or borough Indeed these more general link criteria now take precedence over disaggregation by capacity index since capacity indices are generally aimed primarily at setting link speed flow curves from which a disaggregation of say PCU kms may not be particularly useful 15 179 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 59 2 15 59 3 5120257 Apr 15 Section 15 Disaggregation within SATALL At the end of each run of SATALL or SATSIM a complete set of total network Statistics are calculated and stored within the output UFS file In addition optionally a further set of disaggregate statistics is calculated and stored in UFS as controlled by user set Namelist parameters in the network dat files Thus if BYGRUP T statistics are calculated by link groups see 5 1 7 3 where the groups are defined either as a traffic boroughs if a parameter TFL T or if TFL F b by a N2Q file set as FILN2G N2G files are specified further in Section 15 60 basically they define an index for each node such that links are grouped according to the node index of their B node Which is effectively the way in which links are grouped into traffic boroughs where the name of a link s B node defines its borough number following TfL rules see 5 1 7 2 Finally if BYGRUP T TFL F but no N2G filename has been set FILN2G is blank then no di
44. R ALOG R R 1 0 1 0 IF XBOT NE 0 0 XN R 1 0 XBOT 1 0 END IF and the following table gives values of n for typical DIp parameters where the speeds are in kph and the flows capacities in pcu hr 5120257 Apr 15 15 20 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 9 3 5120257 Apr 15 Section 15 For the range of flows above capacity DIp and SATURN curves both have a linear relationship although the slope of the curve in SATURN is determined from the length of the time period simulated parameter LTP while that for the DTp curve is set by the parameter 8 in the above equation which has units of 1 hours To set up the same slope in SATURN it is therefore necessary to set LTP 15 i e 1 4 of an hour since the slope equals 0 5 LTP Having set up the buffer network the user may now begin to code parts of the network in the format and detail required for a simulation network starting with those nodes where the extra detail is most required and working outward as far as may be required Since any node that appears in both the simulation and buffer networks is ignored in the buffer network nodes may be coded as simulation nodes without having to remove them from the coded buffer network One advantage of coding SATURN networks in this way is that the user gains coding experience by degrees and thereby makes fewer mistakes overall Note that in following this proc
45. We may then select each CSV file in turn and these will be imported as new worksheets into the existing spreadsheet Once they have been loaded as new worksheets we may now select them to be loaded into the reporting columns in the summary worksheet by clicking on the Filter box at the top of each column The summary statistics for that network will then be summarised in the column below EJ Microsoft Excel Summary Report v3 00 xIs JE File Edit View Insert Format Tools Data Window Help HA0002 SATURN Support JWright Atkins 3 Date Created 30 05 05 version 2 00 Convergence Summary for FoF lows GAP 0 302 0 333 Statistics Summary Results FPSOMSGAXS STA EPSOMSGRA STA Matrix totals pcus hr 5013 1 5170 Transient Queues Total pcus 39 5 196 3 lt Proportion carried over gt 0 5 3 0 Once completed Table 1 Scenario Reports shows the summary statistics for two networks side by side as show below 5120257 Apr 15 15 127 Section 15 SATURN MANUAL V1 1 3 Special Options and Facilities El Microsoft Excel Summary Report v3 00 xls e File Edit wiew Insert Format Tools Data Window Help ane ep eee ae oO a eae med drial Had a3 oF fe Jvvright Atkins Oe A 1 5048181 SATURN Support 2 iJWright Atkins 3 Date Created 15 03 07 4 Version 3 00 10 11 12 Convergence Summary for EPSOMYBAAX 3 SSSSSSSSSSSSSSSSSSSSSS 17 Loops M 12 20 Flows g4 5
46. Wolfe Iteration Costs The costs times are stored as a rolling summation of all Frank Wolfe iterations over all simulation assignment loops up to certain limits see below instead of re creating the assigned route flows by an extra SAVEIT assignment Similarly the weights per iteration take into account not only the weights during the assignment stage itself see equation 7 26 but also any averaging between assignment simulation loops associated with DIDDLE AUTOK etc This has the benefit that any secondary analysis e g skimming SATME2 see 13 3 13 etc based on routes is exact not an approximation since it reproduces the precise routes used in the full assignment This therefore reduces but not entirely removes some of the problems associated with e g the uniqueness of skimmed matrices see note 6 15 27 6 The disbenefit is that there may be many more rolling iterations in total than there would be in a SAVEIT assignment which means that a the UFC files are larger and b any secondary analyses take proportionately longer However if the total number of rolling FW iterations becomes too large greater than a amp PARAM parameter NITA_C default 256 then we revert to an extra SAVEIT assignment in any case Note that the total number of Frank Wolfe iterations aggregated over all assignment simulation loops depends on the rate of convergence as well as the values set for MASL and NITA Thus if convergence is
47. a particular origin to a particular destination which use that link It is therefore virtually identical to the Pija factors as used by SATME2 although used in different contexts Forests are a highly preferable method of analysing O D routes for the simple fact that they contain information about ALL routes assigned traffic for that O D pair as opposed to looking at the single route which is currently minimum cost at the end of the assignment process and which may even not have been used in the assignment itself Trees may be built in a number of different ways within P1X SATDB or SATLOOK although the graphical methods within P1X 11 8 3 are generally recommended Forests may be built in either P1X graphically or SATDB numerically Equally they may be built under both stochastic and Wardrop equilibrium style assignments But see remarks in Section 7 2 4 concerning the consistent re creation of randomised costs By contrast an arboretum is defined to be the set of all different routes used by a single O D pair i e the complete set of different trees Thus if an assignment takes 20 iterations it generates 20 trees of which only 5 of these may make up the arboretum The arboretum display option in P1X displays each tree one ata time with data on the fraction of all trios using that route Summed over all iterations or trees Because it uses fewer displays it is preferable to displaying trees one at a time 15 63 SATUR
48. a value of 1 indicates that the link is the first link beyond the entry ramp in a sequence of more than 1 links e g 10 15 in Figure 15 3 4 indicates it is the final link before the exit ramp 16 20 in 15 3 5 that it is the only link in the sequence i e both entry and exit while 2 indicates an intermediate link in a sequence of multiple links e g 15 16 The markers may be displayed as link annotation data via P1X under Properties or otherwise accessed as a data base item within SATDB In addition the lpt files output by SATALL print a list of all links where weaving factors have been applied at each assignment simulation loop with the current values of all relevant data such as Qw X etc The factors may also be displayed in the numerical node information menu in SATLOOK post 10 6 SATTUBA Objectives SATTUBA is a procedure embedded within SATLOOK which enables a set of skimmed cost matrix files to be calculated from a ufs network file and output in a text format which is compatible with the economic appraisal program TUBA More specifically TUBA requires as input a set of matrices giving for each O D pair passenger or vehicle trips distance time and monetary charges These matrices may be further disaggregated by e g user class time period trip purpose etc 15 99 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 41 2 5120257 Apr 15 Section 15 Dis
49. a vis a simulation network is that it has better convergence properties due to the fact that it uses separable cost flow curves see 7 1 3 Conversely simulation networks suffer potential problems of non convergence due to the fact that by allowing for within junction interactions their cost flow curves are non separable Very often this may introduce noise into the solution which makes it difficult to accurately assess the impact of relatively small schemes SATURN 11 has introduced the possibility of creating an intermediate network band referred to as the Peripheral Simulation Area in the diagram above which 15 1 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 1 2 15 1 3 5120257 Apr 15 Section 15 would lie geographically between the central pure simulation network and the outer buffer network and which would be modelled at a simpler and or more aggregate level than the normal simulation but not necessarily as coarse as the buffer network Two options are available for the intermediate region 1 Conversion into a Fixed Cost Curve network FCF 2 Simulation to Buffer Transformation SBT Fixed Cost Curves are described in Sections 15 1 2 to 15 1 6 below and the Simulation to Buffer Transformation in 15 1 7 They are compared in 15 1 8 Network Simplification using Fixed Cost Curves FCF The FCF transformation retains the essential geometry of the simulation network in that i
50. be suitably expanded into an IN profile with say 15 units provided of course that both junctions have the same LCY Simulation Link Flows and Centroid Connectors Simulation Zone Connectors Because of the way in which zones in the simulation network are connected to links not nodes certain ambiguities may arise with respect to the definition of link flows The various possible definitions are illustrated below for a zone Z which is connected to an internal simulation link AB X and Y mark the imaginary points along AB where trips leave and enter Z A B The flow on AB may in theory be defined in five different ways i e the flow along AX the entry flow onto the link XZ the exit flow to the centroid XY the mid link flow ZY the entry flow from the centroid and YB the arrival flow at the stop line at B For uniformity throughout SATURN we assume that the link flow is always taken to be the mid link flow i e the flow on the link once all traffic destined for the zone has been removed and before any new traffic has joined from the centroid Thus as defined the link flow is probably lower than the flow that might be observed on the link in reality although the fact that the link has been connected to a zone implies that the flow level probably does vary along the link This therefore is the definition of link flow as used e g in comparing modelled and observed flows see Sectio
51. be viewed in e g P1X as normal link data In the event that all user classes have the same PCU weight ie 1 0 both measures of time are identical and 4008 is not included Current applications of weighted times include validation of timed routes see 11 7 2 1 and joyrides see 11 8 2 3 Further suggestions are most welcome UNIQUE Combined Queues within the Buffer Network The option UNIQUE was introduced in 10 7 in order to minimise the double counting of V gt C delays in buffer networks in certain circumstances 15 121 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 49 15 49 1 1 5120257 Apr 15 Section 15 More precisely consider a series of links A B C D in the buffer network such that traffic on A B can only exit to C ignoring U turns to A traffic on B C can only exit to D etc etc Hence all links must be assigned the same demand flow V If say A B and B C both had the same capacity C and V gt C then in reality one would expect that a queue of traffic would form on A B at a rate V C but that the capacity on A B would restrict or meter the actual flow to B C to equal C and that therefore there would not be a second queue on B C Hence there should be a queuing delay on the first link but not on any of the flow metered links downstream However prior to 10 7 and UNIQUE the same queue build up and consequent ing delay was imposed on all links A B B_C
52. by setting a parameter CLIMAX T under amp PARAM If CLIMAX T then it is assumed that the speed flow curve for a particular user or vehicle class is fixed at CLICKS independent of the total link flow until the car speed drops below that value at which point the car and other speed flow curves coincide In other words the penalty time imposed under CLICKS is not fixed but gradually reduces from its maximum value at flow equal zero until it goes to zero at the point where the car speed equals CLICKS In almost all cases CLIMAX is used to model fixed speeds for HGV s which are less than car speeds under free flow conditions up to the point where car and HGV speeds become equal Whether or not this is a better representation of the differences between HGV and car speeds is of course up to the user In modelling terms the fixed travel time per link applied to e g HGV s is adjusted within the simulation assignment loops within SATALL at the end of each simulation step effectively at the same time as the link soeed flow curves per turn are updated for the next assignment step via the simulation For example consider as in 15 47 1 a link which is a 1 km long b has a maximum speed CLICKS for HGVs of 100 kph and c a speed flow curve defined with a speed of 120 kph at free flow With CLIMAX F the time penalty for HGVs would be fixed and equal to the difference between 1 100 and 1 120 hours i e 36 30 6 seconds With C
53. by the final simulation as opposed to those calculated by the final assignment DA code 4013 rather than 4003 XCCSK also applies to SKIMDIST i e if T skimmed distances on centroid connectors are assumed to be zero Tolls under SKIMTOLL are in units of pence or strictly speaking defined by the parameter COINS and include all monetary toll components whether defined under the 44444 records or as a KNOBS input See Section 20 N B Since tolls in the sense of explicit monetary tolls were only introduced in version 10 3 SKIMTOLL cannot be used with files created prior to 10 3 15 72 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities Loe fe poy fe ee 5120257 Apr 15 Section 15 By contrast with SKIMTOLL SKIMPEN also extracts data from the 44444 data inputs but only those elements which been defined as times rather than money i e those without a or sign See 6 7 Skimming Using Aggregated SPIDER Networks lf SPIDER T and the network has been built using an aggregated network definition see 15 56 then the algorithm used to build minimum cost trees may be based on either the basic or the aggregated network depending on whether a parameter USESPI F or T respectively The default value set by the program is F but it is generally over written by the value within the preferences file SATLOOKO DAT which may be set by the user Or see the sub section below for a further method for s
54. can be somewhat dangerous to use in that punching errors may go undetected and lead to extra external nodes being 15 30 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 erroneously added Its use is recommended for very simple networks for example a network consisting of a single simulation node connected to n un coded external nodes set up to simulate an n way junction in isolation an example of which is given below or for networks set up from recoding existing buffer networks or when coding using PMAKE Section 18 The AUTOZ option removes the need to explicitly define simulation centroid connectors 6 5 to external simulation nodes by automatically attaching centroid connectors to every link terminating at an external simulation node and assuming that the zone has the same number as the external node Thus in the above example where node 99 is an external node connected to internal simulation node 22 a zone numbered 99 would be created attached to link 99 22 at node 99 in exactly the same way as if a record 99 99 22 were included in the 22222 data as described under Section 6 5 When using AUTOZ all connections as defined under 22222 should be internal connections otherwise there will be duplication and AUTOZ should only be invoked when ALL external nodes are pure cordon points not when they are links between the simulation and buffer networks In effect this restr
55. carry out the actual assignment within the assignment simulation loops 1 a buffer network with a fixed trip matrix 2 post 10 9 a simulation network where MASL 1 i e SATALL has only been through a single assignment and the routes costs used on that assignment are retained or 3 UFC109 T and the total number of assignment iterations is relatively small see 15 23 3 below Otherwise and very often the above conditions are not satisfied an extra SAVEIT assignment needs to be carried out by SATALL in order to re create route flows and to create the UFC cost file Thus the SAVEIT assignment is a final complete Frank Wolfe assignment stage carried out at the end of the simulation assignment loops using the final set of speed flow curves and starting in effect with a blank sheet of paper e g the initial all or nothing assignment uses free flow costs The set of iterative costs and weights stored in the UFC file and used in the subsequent analyses will be those derived from the SAVEIT assignment as opposed to those from the true assignment Specifically under elastic assignment the final assignment uses the fixed trip matrix generated by the final elastic assignment Almost all options which may be used to improve the normal assignment within the assignment simulation loops may also be invoked by the SAVEIT assignment for example an aggregated SPIDER network may be used under SAVEIT a
56. clearly nowhere near minimum The expectation is that the extra CPU involved in building two trees instead of one will be justified by the early elimination of bad paths and therefore not only reduce residual flows but accelerate convergence Improved Frank Wolfe algorithms which incorporate the above ideas are currently being developed and tested but are not yet available to users 15 176 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 57 6 15 58 15 58 1 5120257 Apr 15 Section 15 Avoiding Residual Flows Choice of Assignment Algorithms Whereas residual flows may be an intrinsic problem created by the Frank Wolfe algorithm the same problems do not occur with all traffic assignment algorithms Thus they are virtually non existent under OBA and very much less common under path based algorithms where social pressure based algorithms see Appendix H preferentially remove residual flows In addition the Partan variant of Frank Wolfe 7 11 7 tends to reduce the occurrence of residual flows due to its ability to include backward steps which are able to entirely remove the contributions from early iterations It is therefore automatically invoked during a SUC SAVEIT assignment 15 23 4 N B To use Partan during the MUC SAVEIT assignment you must set the parameter SPARTA T it is not automatically invoked as with SUC See 15 23 4 Equally the use of incremental assignment 7 11 13 during the i
57. coded as W Thus in Figure 15 5 it would be applied to turns 10 11 19 11 19 20 19 20 3 and 19 20 4 It would not however be applied to the turns corresponding to entry into the first weaving link i e turns 2 10 11 and 1 10 11 in Figure 15 5 The factor is in effect applied immediately after the saturation flows are set and at the same time as the blocking back factor is applied i e step 2 in Section 8 2 1 Note that the reduction factor is equally applied to all turns at intermediate nodes if any between the entry and exit nodes Note that the weaving reduction is applied in addition to any other capacity reducing effects such as give ways or blocking back 15 97 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 40 4 5 Simulation Delays 15 40 5 15 40 6 15 40 7 5120257 Apr 15 Section 15 Weaving does not of necessity add extra delays to traffic although there are three ways in which extra simulation delays may result Firstly tf a link becomes over capacity due to weaving then queuing delays will be imposed Secondly if the weaving links are subject to link capacity restraint functions see 6 4 12 then the link or pinch point capacity used in equation 6 2 is also reduced in accordance with Equation 15 9 above leading to in effect a reduction in cruise speed for a given flow Finally if a Q marker has been used on an intermediate link see App Q then the capac
58. distances the second contains times the third contains toll charges if any exist and the fourth contains penalties if any exist Units are the defaults as specified by TUBA distance is in kilometres time and penalties are in hours and tolls are in pence The format used is TUBA Format 1 see Appendix C of the TUBA User Manual for more details Essentially this outputs all O D cells one record per origin in comma separated format If required options to input under formats 2 or 3 could be provided Multiple User Class Networks If the network has multiple user classes NOMADS gt 1 then separate TUBA data files will probably need to be produced for each individual user class Thus Sattuba net UC 2 processes data for user class 2 from the MUC network file net ufs to produce Net uc2_d txt net uc2_t txt etc etc Equally Sattuba net UC processes data for all user classes See 15 41 4 2 Options within SATTUBA We describe here three alternative options within SATTUBA the use of a control file the use of distinct user classes and alternative output matrix file formats The Control File The precise format of the output txt files may be modified by a number of parameters and or options contained as Namelist parameters in the SATLOOK preferences file satlookO dat 11 17 2 Alternatively a different preferences or control file may be defined on the command line by e g Sattuba net KR control in
59. externally by the user via say Excel prior to its use in P1X Disaggregate Network Summary Statistics General Principles Network statistics such as total PCU hrs total PCU kms etc are automatically calculated over all links by SATALL and SATSIM with a split between e g simulation links buffer links etc as illustrated by the tables in Sections 17 8 and 17 9 In addition to total flows flows are always disaggregated into the following categories if they exist 1 bus flows 2 pre loaded flows 3 PASSQ flows 4 all user class flows and 5 flows exclusively from the trip matrix Therefore the standard output statistics always include the total PCU kms by pre loaded flows or by user class 3 etc etc However it is also possible to optionally obtain a further disaggregation of the same statistics by sub sets of links and or by sub sets of flows either calculated within SATALL SATSIM or afterwards using SATLOOK Note that the sub sets of flows are effectively fixed and used in each level of link disaggregation Thus the main choices to be made by the user are how to define the disaggregation of links Traditionally links were disaggregated into sub sets according to their capacity indices but post 11 2 8 it is possible to define a much wider range of criteria to set link sub sets For example links may be grouped into self contained sectors or traffic boroughs see 5 1 7 1 and 5 1 7 2 and statistics such as total
60. firstly be defined using the KNOBS facility see 15 14 any of the 3 input methods may be used and a proportionality factor BTKNOB b k set gt 0 where b refers to a bus company and k to a KNOB data set 1 KNOBS The units of BIKNOB are assumed to be seconds per whatever units that particular knob data field is in Again BIKNOB may be defined within the amp PARAM namelist records 6 3 3 Note that in using namelist input to set BTKNOB which is a 2 dimensional array you may need to use the array based input so that BTKNOB 3 0 3 0 0 4 0 would set the elements 3 1 3 2 and 3 3 to 0 3 0 0 and 4 0 respectively See note 17 Appendix A In fact BIKNOB is the only variable to which array based inputs may be applied Both methods are fairly aggregate even crude in that they do not allow you to define stopping times by links by bus route unless you have one route per company which is not very practical However they are a start and all requests for more will be listened to 15 113 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 45 15 46 15 46 1 5120257 Apr 15 Section 15 Representing Walk Pedestrian Networks Traditionally SATURN networks represent roads down which cars travel and their travel speeds are vehicle speeds However there is no hard and fast reason why every link in a SATURN network should be a road link and it is quite possible to fool SATURN into tr
61. function of the cln file is to supply link numbers not network structure Viewing COBA Link Numbers The link numbers used in the output COBA network may be displayed Version 10 5 and onwards via P1X and or SATDB but only at the moment if they are based on SATURN assignment link numbers as opposed to user set KNOBS data Thus they appear as option 12 under the Miscellaneous Data Input sub menu from the SATDB top menu In addition the links used may be selected under Link Selection in SATDB Recall that for 2 way links only one direction is used in general A B rather than B A where A has a lower node number than B To display the user set link numbers simply access the KNOBS data element used preferably with the links selected as above Alternative Sequential COBA Node Numbers While it is generally preferable to use the standard SATURN node numbering system within COBA networks it is not always possible In particular COBA requires that node number have a maximum of 4 digits so that if your SATURN network uses 5 digit numbers then they will have to be reduced converted to a system that uses a maximum of 4 One might well ask why COBA isn t upgraded to accept 5 digit node numbers rather than SATURN having to resolve the problem mais c est la vie There are two alternative node numbering systems that may be used within SATCOBA to avoid 5 digit node numbers The first is based on the sequential node
62. image would be very chunky That problem could be avoided by creating outside SATURN a omp which covered just the 20x20 area with the full resolution of 2 000 x 2 000 pixels However that would not be a very useful background for a window of 1 km x 1 km lt is of course possible within P1X to prepare several different input bmp files and to swap them over depending on the current window but it is not highly satisfactory Such problems could also be removed by increasing the maximum dimensions which SATURN can handle e g to go from 2001 x 2002 to 10 000 x 10 000 and this can be done easily enough when compiling the program However this may create other problems in that a omp file of 10 000 x 10 000 pixels requires 6 x 10 bytes i e 0 6 GigaBytes within P1X which might in combination with all the other demands from P1X exceed the RAM provided on most machines and therefore slow down the overall execution speed dramatically In addition even if there were sufficient internal RAM the cpu time required to input and manipulate very large omp files may still be excessive for most user requirements 15 112 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 44 5120257 Apr 15 Section 15 The size and resolution of omp files may be easily manipulated using standard Windows graphics packages such as MS Paint or MS Picture Manager for example Defining Extra Bus Travel Times BUSSPK and BTKNO
63. in fact sequential Records need not be in numerical order of zones i e the first number given is always increasing although this is generally the most convenient way to create such files Duplication i e assigning the same zone to two different groups is not allowed although it may not always be checked A hyphen in front of a zone name negative numbers may be used to indicate a range of zones Thus two successive records 9 1 ae 15 181 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 60 3 15 60 4 5120257 Apr 15 Section 15 would indicate that all zone names in the range 10 through 19 would be assigned to group 2 and that zone 9 would be in group 1 Note that 19 need not necessarily be a valid zone name itself it simply represents an upper limit in which case the true upper limit would be the maximum zone name lower than 19 The lower value of the range is the previous upper limit plus one If a negative number is used to indicate an interval the absolute value of the negative number must be greater than the absolute of the previous number in the list If as above a positive number is used e g 9 to set the previous line that zone name must exist Therefore it is recommended that you use either all intervals negative numbers or include all zone names in the Z2 file using the philosophy that the point of using intervals is for the process not to fail and the point of
64. in the middle of a link along an O D path as in fact must virtually always occur the loaded flow is taken pro rata depending on the length of that link Non discontinuous Speed Flow Curves the Kinky Option Generally as described in Section 5 4 and elsewhere SATURN speed flow or cost flow curves are assumed to follow a power law for flows up to capacity and to be linear thereafter equations 5 1a and 5 1b respectively Thus there is a discontinuity in the slope introduced at V C although the times or costs themselves are continuous Generally the discontinuity does not create problems within the assignment algorithms and the shift to a linear form is quite realistic particularly bearing in mind that a power law curve with say power 5 goes very rapidly towards infinity for V gt gt C a not very realistic forecast which can have serious consequences for scheme benefits However there may be circumstances when the user does wish to extend the simple power law relationship over flows from zero to infinity for example in modelling networks with so called BPR curves or when doing system optimal assignment where the discontinuity in slope may be an algorithmic problem see 7 11 9 This is simply done by setting a parameter KINKY to FALSE in the network dat file or in control files elsewhere in which case equation 5 1a holds over the full range of flows for actual times and 7 19a holds for the full range of marginal costs
65. lanes It is however possible to use the 33333 data cards to define extra simulation link data which is not required by the simulation proper but which might be useful under other circumstances One example of this is the link capacity index which is used to distinguish certain classes of links in summary statistics If a link A B is included in the buffer network data with a capacity index of say 5 but was previously defined as a simulation link the Capacity index of 5 is assumed to apply as well to the simulation link A B Using the BEAKER option see 6 3 1 the index may also be associated with turns out of A B setting BEAKER to TRUE is highly recommended Similarly any extra KNOBS data defined for duplicates of simulation links are also assumed to apply to those links See Section 15 14 A further important application concerns external simulation links i e the simulation link from an internal simulation node A to an external simulation node B By definition the travel time on the in bound link B A is fixed being a simulation link with in effect infinite capacity any additional delays or capacity restraint on that link are associated with turning movements at A On the other hand assuming a fixed travel time and infinite capacity on the out bound direction A B would not be entirely realistic since turning movements at B are not included in the simulation It is thus possible to define flow de
66. matrix equally divided into six user classes then SATCOST will create a stacked ufm matrix with six levels one per user class each approximately equal to the cost matrix for a single user class Thus the fact that the trip matrix is divided by six per user class does not imply that the cost matrices are equally factored several alternative bat files are provided based on Forest Skimming Option 9 within SATLOOK see 11 11 9 In particular SATC_AV skims average costs from a forest 15 27 3 SATC_MAR skims marginal costs but only from networks which were assigned under system optimal conditions see 7 11 9 SATC_ITP produces a minimum cost matrix a la SATCOST but over multiple time periods see Section 17 SKIMTIME skims averaged o d times in seconds from a forest as described in 15 27 3 15 71 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities ig27 21 5120257 Apr 15 Section 15 SKIMDIST skims averaged o d distances in metres from a forest SKIMTOLL skims averaged o d tolls in pence see Section 20 3 from a forest SKIMPEN skims averaged o d time penalties in seconds as defined within the 44444 data records from a forest SKIM_ALL combines SKIMTIME SKIMDIST SKIMTOLL and or SKIMPEN into a single routine which skims all 3 or 4 quantities simultaneously which means that the CPU time is reduced by a factor of roughly 3 4 or 2 if there are no tolls included in
67. models see 7 8 6 and 15 27 6 Select Link Analysis see 15 19 or PIJA analysis 13 3 12 For example the total flows on a link generated by a select link analysis may not exactly equal those generated by the original assignment However it also needs to be borne in mind that the errors associated with SAVEIT are just one extra source of noise to be added to the non convergence errors from SATALL proper see 2 1 and 9 5 Essentially the SAVEIT assignment is an approximation to an approximation Therefore a perfect SAVEIT assignment is not a guarantee of an error free economic evaluation although it may help Comparison Statistics SAVEIT vrs Original Assignment In order to assess the consistency of the two different assignments a set of difference statistics is generated and printed at the end of the SAVEIT assignment comparing the SAVEIT link flows with the true assigned link flows These include The average GEH difference statistic comparing the as assigned flows and the SAVEIT flows The mean average absolute difference between the flows expressed as a percentage The relative standard deviation The average absolute difference in pcu hr The percentage difference between the total pcu hrs calculated using the assigned and SAVEIT flows Ditto using distance instead of time Ditto using assignment cost instead of time The last three statistics new in 10 6 may be
68. never going to feature in minimum cost O D paths then they may be eliminated before the tree building takes place In particular if a link has zero flow then it can never be part of a used path for an O D cell with positive trios and it may be ruled out a priori For example if we are re constructing O D paths post assignment as part of a Select Link Assignment see 15 23 and or 11 8 1 then we are only interested in those paths which carry positive flows and clearly any link which we already know has zero flow cannot be part of those paths Thus before carrying out SLA we remove all links with zero flow in total On the other hand if we are skimming say O D distance or time then it is possible for a link with zero flow to be part of a min cost O D path where the O D itself has zero flow Equally during the extra SAVEIT assignment where we have already carried out a full assignment as part of the assignment simulation loops we know which links are unused and these can be eliminated within SAVEIT Although strictly speaking it is possible that due to poor convergence a link could be used during a SAVEIT assignment when it was never used during the full assignment At the moment the trick of eliminating zero flow links is used in the following situations 1 SAVEIT assignments see 15 23 2 2 SAVUFO calculations see 22 5 3 3 Select Link Analysis SLA with P1X see 11 8 1 12 4 SATCH cordoned matrices see 15 56 7 2
69. not therefore produce route flows which are biased by origin Its outputs might therefore be charitably described as plausible but never perfect The situation however becomes worse if we consider not just the OD route patterns in a single network but any comparison of the route flows in two networks which differ slightly from one another Here the noise generated by the above two problems may render any comparisons extremely tenuous To a certain extent the problems with route flows are simply an inevitable consequence of the fact that more you disaggregate data the more unreliably it becomes There are far more route flows than say link flows and the flows per route are much smaller than the flows per link These problems are however aggravated by the problems of non uniqueness and the lack of an acceptable behavioural model of route choice What is required possibly is an extension to Wardrop Equilibrium to deal with route choice and which would operate at a far more disaggregate level than total link flows This issue is discussed further in the following section 15 23 9 Unique Route Flows The Principle of Proportionality One method in theory at least to define a unique set of path flows within a Wardrop Equilibrium solution is to require that the path flows satisfy the 15 58 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities oroportionality condition see for example various artic
70. number in the SATURN assignment network so there will be gaps in the numbers An alternative system of user set link numbers is described in 15 42 3 Secondly SATCOBA then calculates the total flow per COBA link with the flow for a 2 way link being the sum of its two directional flows Furthermore since COBA wants flows over say 24 hours or 12 etc etc the flows are factored by a user set parameter COBAF which is defined under amp PARAM in the original network dat file default 1 0 and or within the SATCOBA control file See 15 42 2 via COBAF1 COBAF2 etc 15 103 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 42 2 5120257 Apr 15 Section 15 By default the flows output are total flows and therefore include all fixed flow etc contributions although there are alternative options MUC and MVC by which flows by individual user or vehicle classes may be output see 15 42 2 below In addition the units may be either pcu hr or vph In addition since COBA flows would normally be the weighted sum of flows from say an AM off peak and PM network SATCOBA accepts as input one or more networks i e time periods and outputs a single flow which is the weighted sum of each individual network flow It is assumed that all networks have the same topology Alternatively if the parameter SUMNET F 15 42 2 each network flow is output separately Next SATCOBA generates a partial data set whi
71. numbers as used internally by P1X to create map networks whereby each sequential number refers either to a zone the first NCENTS entries or a junction whether buffer or simulation Note that map sequential numbers may be viewed within the SATDB node data base as 15 107 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 43 15 43 1 5120257 Apr 15 Section 15 accessed within P1X by selecting the appropriate entry from the list of node attributes Sequential numbers are selected within SATCOBA by setting NAMES F in the control file 15 42 2 or alternatively it will be done automatically if the maximum node number exceeds 9999 The second system uses an explicit input file to convert SATURN node numbers into a more compressed system which could indeed be based on pure sequential numbers as above but any arbitrary conversion system may be used To select this option a set NAMES F as above but b define the conversion file filename as FILNOD within the control file 15 42 2 The conversion file consists of a series of records one per real node i e zones are not included as they do not appear in COBA outputs each of which contains a a real node name which may exceed 5 digits and b its equivalent output number 4 digits or less All COBA node number outputs are automatically converted to the new system The main advantage of the second system is that it may applied to any nu
72. of the lpn file If for example the crow fly distances are consistently around 10 times shorter than the coded distances then it is presumed that XYUNIT should be 10 times greater CROWCC Zero Distance Buffer Centroid Connectors The above rule for replacing an input buffer distance of zero by the crow fly value traditionally applied to both real buffer links and buffer centroid connectors However while it may make sense to have a positive distance for real links it may be quite legitimate to have centroid connectors which are purely nominal and therefore have zero distance plus presumably zero time An option introduced in version 10 7 allows users the choice as to whether or not buffer centroid connectors may be assigned a distance of zero Thus if CROWCC T set in amp PARAM of a network dat file and SHANDY T a crow fly distance replaces buffer centroid connectors with an input value of zero If CROWCC F an input distance of zero is accepted For most users CROWCC F is likely to be the preferred option However the default option prior to 10 7 was effectively T so for upwards compatibility the 15 28 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 11 5120257 Apr 15 Section 15 default value of CROWCC was set to T at that point in time Subsequently release 10 9 the default was changed to F We further note that setting CROWCC T may have certain potentially negative conseque
73. part into a pure buffer network e g to carry out very simple sensitivity testing or to convert it for use in another suite of programs so SATURN not good enough for you eh Essentially this requires that link cruise times plus junction delays are converted into the best equivalent buffer speed flow curves which since they cannot distinguish between different turning movements must of necessity be suitably weighted averages The averaging of delays may be carried out using routines within SATDB and data for each simulation link dumped to an ASCII file A special purpose bat plus key file is provided to do this Type SATBUF net to produce an ASCII file net buf which contains for each simulation link A B a single record containing Its A node Its B node The average free flow time in seconds The average time at link capacity in seconds The distance in metres The link capacity in pcu hr The weighted flow delay power n The times above include both cruise time along the link plus a flow weighted average of the delays to each individual exit turn d V d gt V where di delay for turn i Vi Simulated actual flow for turn i Thus if you have a simulated right turn with a very long delay but consequently a very low flow this will have relatively little effect on the delays which would be modelled in the buffer network so that in a buffer network representation you could expect to ove
74. proportion of CPU expended on path building loading relative to that spent in junction simulation and the re estimation of paths for the final assignment The overall reductions in CPU expenditure may be substantial for example for Model 3 using Multi Core FW with NA reduces the model run time compared to the standard FW technique from 4 5 hours to less than 30 minutes with the same level of convergence Further information on the practical benefits of Network Aggregation techniques may be found in the Appendix S 15 56 7 Other Applications of Aggregate Networks Thus far we have concentrated on how aggregated networks may be used to reduce the cpu time required to a build minimum cost trees and b load O D trios onto those paths They may however be used effectively in several post assignment analyses as well as other modelling issues 15 56 7 1 Tracing Paths in Aggregate Networks lf an analysis option of min cost O D paths wishes to trace a path which in the basic network follows a link sequence A B C X Y Z then it requires 25 steps If on the other hand the network has been aggregated such that the equivalent aggregated path is A G M R Z then only 4 steps are required clearly potentially much faster 5120257 Apr 15 15 171 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 13 96 2 For example O D skims of say times along a forest may equally be calculated on an aggregated netwo
75. slow and the maximum number of loops MASL is used and the maximum number of Iterations per loop are also used then the total number of iterations equals MASL times NITA Therefore reducing MASL and or NITA will make it more likely that the option will be used although achieving an acceptable level of convergence is certainly a more important objective See Section 9 5 for advice on improving convergence and 9 5 4 on the choice of NITA 15 23 3 2 UFC109 or UFC111 T Storing UFC Link Times under MUC 5120257 Apr 15 Section 15 Under multiple user classes if either UFC109 or UFC111 T the output UFC file stores the sets of link times per iteration as opposed to link generalised costs by 15 53 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 23 4 5120257 Apr 15 Section 15 both iteration and user class This is possible because the times per iteration are constant between all user classes on the same Frank Wolfe iteration the costs may differ but only because the fixed costs per user class differ and since the fixed costs are fixed throughout by definition it is straightforward to construct the costs per iteration UC by adding UFC stored times per iteration to fixed costs by user Class This means that the UFC files produced under UFC109 111 will be reduced in size by a factor of 1 NOMADS with only a very small overhead in reconstructing costs as required for secondary analysis However for a
76. strategy with the strategy chosen determined by the number of loops undertaken by the demand model This provides the user with the flexibility to switch between strategies depending on whether the demand model is in an early stage e g loops 1 to 5 for example middle stage e g loops 6 to 10 or late stage loops 11 onwards and approaching completion as illustrated below Early Middle Late Demand Model Loop 1to5 6 to 10 11 to 15 KONSTP 1 1 1 STPGAP 10 2 5 0 05 ISTOP 90 95 98 MET 0 0 0 SAVEIT F T T UNCRTS 10 2 5 0 05 NISTOP 1 1 2 MASL 10 40 80 NITA_S 25 100 250 Each strategy is identified by a LoopThreshold Y where Y is the demand model loop which that strategy is used If more than one strategy is specified the Loop Thresholds must be provided in ascending order Within each strategy or LoopThreshold the following row s provide the parameters to be transferred to the XCP file depending on the GAP SD value reported in the Demand Model convergence file FILGAP Each row starts with GAPValue Z where Z is the GAP SD threshold that identifies the parameter s to be adopted for the next loop if the demand model convergence is less than the value of Z The parameters for each GAP SD value must be contained on the same row and each parameter separated by a comma 15 154 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities In operation CASSINI will Read the demand model convergence fil
77. strict so that a second rule has been added Thus rule 1 for a nearside bus lane if a bus route makes a turn at the downstream end of the link which is allowed to use lane 1 given the input turn lane specifications on that link then it is allocated to the bus lane otherwise it is assumed not to use the bus lane Thus for example a bus route which turns right drive on the left at the end of a link would not be able to use a nearside bus lane if the normal right turns were only allowed from lane 2 Similarly an offside bus lane may only be used by a route whose exit turn uses the highest most offside lane e g left turning buses would be excluded from an offside bus lane The second rule termed the 1 1 rule relaxes the above criteria by increasing both the critical lane and exit turn by 1 Thus if a bus route takes the second exit from the nearside and if that turn can use the second lane then that route may use the nearside bus lane on the link For example a bus which is going straight ahead second turn at a 4 arm junction may use a nearside bus lane if ahead traffic can use lane 2 Similar rules apply to offside bus lanes but in reverse At the moment the model does not fully consider the continuity of nearside and offside bus lanes in allocating buses to bus lanes Thus buses on a nearside bus lane on link AB may transfer seamlessly to an offside bus lane on link BC and back again to a nearside lane on CD Furtherm
78. system used within SATURN assignment networks However it is also possible for the user to define their own set of link numbers using the KNOBS input facility to SATNET see 15 14 This option is controlled by the namelist parameter KNOB in the satcoba control file 15 42 2 Thus if KNOB 1 then the link numbers are those defined within KNOBS field 1 etc etc If the input KNOBS value for a particular link is O then that link is not included in the newly created satcoba network this facility therefore allows the user to select those links which are to be included in the coba files via KNOBS data The KNOBS data is by default that input via SATNET into the network ufs files but it may also be input directly into SATCOBA via the namelist parameter FILKNB 15 42 2 which defines the name of an input file Format conventions for the file FILKNB are as per inputs to SATNET 15 14 5 Note that KNOBS data are essentially input and stored as real data but when used in this context they are rounded off to the nearest integer Common COBA Link Numbers in Multiple Networks One very useful application of using KNOBS data to define link numbers is that it allows two or more networks e g a do minimum and a do something to use the same definitions of link numbers To do so the user must first create a text data file for the base network which contains one record per COBA link containing three integers the link A n
79. that junction This may sound vague it is intended to be However most of the time the choice of LCY at non signalised intersections is unlikely to significantly affect the results so that if there appear to be two important controlling signals choose one or the other and don t worry about it At certain points in the standard node link output table warnings are given if a particular link has different values of LCY at its upstream and downstream nodes In particular the SATLOOK table of simulation node properties 11 1 1 contains a line in the link properties which indicates such links The output is in the form of s where the higher number of s the greater the potential impact Thus blank implies equal values implies unequal with signals at neither end is signals upstream but not downstream is signals downstream and is signals at both ends The logic is that profiles and co ordination are most important at signals and the number of s reflects this 15 39 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 16 15 16 1 5120257 Apr 15 Section 15 In addition release 11 2 4 introduced a new test to detect a simulation node with say LCY 60 while all its immediate neighbours had LCY 70 Serious Warning 183 Note that having different values of NUC at two adjacent junctions has no real effect on the OUT IN transformation since an OUT profile evaluated with say 10 time units would
80. the nodes in the walk network have the same or very close co ordinates to real junctions since there will be a high degree of overlap between the walk network and the road network This may be avoided by assigning a unique set of capacity indices to the walk links a good idea anyway and then excluding those capacity indices from the network link plots as described in 11 6 1 4 and or note 4 11 6 4 DBDUMP amp P1XDUMP Dumping Link Data to Text Files DBDUMP Dumping Data via SATDB A batch file dodump bat based on the program SATDB has been set up in order to provide a simple method to dump selected link data from a binary ufs file into an ascii text file For example the command Dbdump net flows txt 4503 dumps the demand flows DA code 4503 from net ufs into a file flows txt following the rules described in 11 10 9 Various options described below are provided to control the precise format and contents etc of the output file Tokens on the command line may be divided into two types DAcodes for output data items 15 114 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 Options DA codes are always given as numerical values For a full list of the DA codes within a ufs file please consult Appendix J Note in particular that codes such as 3808 to represent actual flow by user class 1 are also permitted see 15 21 4 Options are always represent
81. the definition of generalised cost Time penalties are only output if they exist SKIMDA skims a particular property identified by its DA code hence a general purpose skim routine which could be used to skim time distances etc etc by using the requisite DA code SATTUBA skims time distance and or tolls directly to a series of ascii files in various TUBA formats see Section 15 41 for further details For further details on file format conventions etc please type the names above Note also that routines SKIMTIME to SATTUBA as listed above may all take advantage of multiple processors if available see 15 53 3 2 The Definition of Skimmed Cost The following notes may help clarify exactly how the skimmed cost is defined in certain of the above batch files Under SKIMTIME times are equal to the real times along links and or turns plus by default any penalty times which may have been added under the 44444 restrictions see 6 7 However post 10 6 the 44444 penalties may be excluded if a parameter USETP is set to F in the preferences file SATLOOKO DAT Equally if the CLICKS option is being used the link times will use the CLICKS rules if a parameter CLICKY T in SATLOOKO DAT which by default it is See also 15 24 4 Finally skimmed times on centroid connectors may be excluded by setting them to zero if a parameter XCCSK T in SATLOOKO dat 15 41 5 In addition times under SKIMTIME are those calculated
82. the flow on link a as Equation 15 16 V c V V p a In this section we generalise the concept to allow for interactions between different streams of traffic and therefore non separable cost flow functions as modelled by the simulation stage within SATURN We use the acronym MECC to stand for Marginal External Cost of Congestion However the basic underlying concept of marginal cost is unchanged it is the extra cost imposed on all trips by the addition of one extra pcu N B pcu not vehicle on a particular link where a link may be either a road or a simulated turn With separable costs the only other vehicles which are affected by an extra vehicle on link a are those vehicles already on link a with non separable costs the affected vehicles may be on other links Unfortunately since SATURN does not generate explicit non separable cost flow curves of the form ca V where V represents the complete vector of all link flows we must resort to simulation We recall that non separable or interaction costs only arise from turning movements at simulation nodes For buffer links and pure simulation links there are no direct interactions and equations such as 7 46 may still be applied The basic method used to calculate marginal costs for simulation turns is to add one pcu per turn re simulate that individual node and to calculate the changed costs on all turns and or links at that simulation node It is carr
83. the simulation network However in the latter case the effect may not be what was desired For example consider the following schematic network where E represents both an external simulation node and a node which is part of the buffer network S is an internal simulation node and B represents one or more nodes in the buffer network connected to E Let Z be a zone that is connected only via a 22222 record to the two way simulation link E S and not at all via a 33333 buffer record In this case trips from the origin zone Z can only enter the network at E in the direction E S and similarly exit to the destination zone Z at E having come from S They cannot go directly to come directly from B By contrast if Z were connected to E as a 33333 buffer centroid connector then the origin trips would enter at E and have an immediate choice between both B and S Equally the destination trips to Z would exit from E having come from either B or S In general terms the latter is probably what the user would prefer in which case it is therefore better to define the centroid connector from Z as a buffer connection to E rather than as a simulation connection to E S i e it should be included within the 33333 cards rather than the 22222 cards described in 6 5 and 6 6 15 29 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 12 5120257 Apr 15 Section 15 2 The external simulation nodes must also be includ
84. to date releases of SATURN since some of the features listed below are fairly recent additions QUIET This option enables SATURN programs such as SATALL to run totally in the background without interrupting anything else See 14 9 NDPS This controls the number of decimal places used to output skimmed matrices in TUBA Format 2 Large values e g 4 are recommended to avoid convergence problems due to rounding off but in older releases of SATURN this could cause problems of overflow if a numerical skim value required more than 10 columns including decimal places Corrected in 10 7 The current default number of decimal places is 5 See 10 15 2 and 15 41 4 DIADEM parameter Setting DIADEM T under amp OPTION N B not amp PARAM in a network dat file at the same time that UPDATE and or WSTART are also T means that if the file to be updated as set in UPFILE does not exist UPDATE and or WSTART are ignored Normally a missing UPFILE is a semi fatal error In the context of DIADEM this allows the same network dat file to be used to build a network for both the initial assignment and for later assignments where the UPDATE WSTART options may be invoked to update warm start the previous network See 6 1 15 137 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 52 5120257 Apr 15 Section 15 XCL ON COMMAND LINES This feature allows more than 9 arguments per command line In the particular contex
85. to match the precise definition of the counts used e g demand or actual flows may be used actual probably makes more sense in general bus flows may be included or excluded a single user class flow may be selected etc etc Note that Validation being newer provides more options than SATLOOK On the other hand SATLOOK is probably easier to run with a key file or as part of an extended batch file Alternatively both counts and flows may be read into SATDB and the standard Statistical options to compare two data columns invoked Users may wish to define their own difference measures based on the column manipulation facilities within SATDB Within SATDB the user may select either actual or demand flows as preferred Finally P1X can also display difference statistics graphically under link annotation Two standard items are ABS ERRORS which is the difference between counts and actual flows and REL ERRORS which gives the relative differences as a percentage GEH Statistics With one exception the output comparison statistics are standard and Straightforward the exception being what is referred to as The GEH statistic This is a statistic first suggested to me by Geoff Havers of the Greater London Council which is useful in comparing two different values of flow on a link V1 and V2 It is defined by GEH V V 0 5 V V lt may most easily be thought of as the square root of the product of the absolute
86. using a zone by zone list is that you want the process to warn you about missing elements by failing Errors occur and are noted if a record does not consist of two integers if a zone cannot be identified excluding negative values above and if some zones are not assigned to groups These may or may not result in the operation being rejected Blank records are allowed and ignored as our comments i e records with a in column 1 In order to process a Z2G file the zone names and their number must already be Known but the set of group names and their total number are only known and fully specified after the Z2G file has been processed Note that the Z2G format also corresponds to a simplified version of the Records 2 used by the batch file MXM5 see Appendix W 3 FILN2 Node Aggregation N2G Files which map nodes into more aggregate groups follow the same specifications as for zonal aggregation files as described in 15 60 2 two integer values in free format with the obvious caveat that the first integer value per record is a node number not a zone number The use of negative node numbers to indicate ranges is also allowed FILL2 Link Aggregation L2G Links may be directly mapped into groups of links as opposed to using their B node to define the mapping via an L2G etc file where the default file extension L2G signifies a file which gives the mappings of links into groups L2G files contain 3 free f
87. versions programmed for SATURN 8 as part of a research project They are provided primarily for experimentation and their reliability cannot be guaranteed Their choice is governed by the Namelist parameter MYTVV set in the network dat files with a default post 10 9 of 5 previously 1 The basic equi saturation policy essentially follows the classic Webster approach of attempting to minimise the maximum volume capacity ratio by turn by adjusting green splits There are therefore only minor differences between options 1 and 2 which mostly occur in complex situations with lane sharing overlapping stages etc Delay minimisation as the name implies attempts to minimise total vehicle delay at the intersection Since it uses analytical approximations to calculate SATURN delays it will not necessarily lead to a true optimum PO is based on the elegant principle put forward by Mike Smith University of York of equating the product of saturation flow times delay on competing arms Again given the complexities at signals as represented within SATURN our version is not necessarily a pure application of PO It differs from the first three options in that it does not explicitly set out to produce a true local optimum but to set the signals such that in conjunction with the consequent re assignment of traffic the total network travel times will be reduced Finally equi saturation Mark 2 as introduced in 10 1 has the same general objectiv
88. very similar times with very little improvement in travel time However it may be a very useful calibration validation exercise to check that this is indeed the case since large deviations between observed and optimised stage times at an individual node might well be a very good indication that there is something wrong e g that the node has been miscoded or that the assigned flows are well out etc etc Convergence Statistics for Signal Optimisation Whether or not the green splits at signals have actually been optimised it is possible to calculate the maximum possible improvement in the V C ratio per turns at signalised nodes These calculations are carried out at the end of every run of SATALL and the improvements per node are saved on the output UFS files as 15 83 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 32 5120257 Apr 15 Section 15 well as the maximum time change per stage in order to achieve optimisation The LPT file contains a global summary of the potential improvements In addition it is also possible within the P1X Convergence Menu 11 15 to list the 10 nodes with the maximum potential V C improvements and to highlight them Note that those nodes with poorly set stage times are also likely to be the same nodes that cause convergence problems for the assignment simulation loops and therefore optimising those signals may significantly improve overall convergence See note 9 in 9
89. which case the file control dat defines the parameters The following namelist variables may be used EFORM Logical If TRUE the data is output using E Formats Default F NDPS Integer Number of decimal places printed subject to certain minima Default 4 USETP Logical If TRUE 44444 time penalties are included within the skimmed times See 15 24 4 Default T CLICKY Logical If TRUE skimmed times by user class include any possible extra times due to CLICKS See 15 24 4 Default T 15 101 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities XCCSK Logical If TRUE times and distances on all centroid connectors effectively only buffer centroids since simulation centroids have zero time and distance by definition are excluded from the skims by setting them to zero However any tolls on centroid connectors are included as set See 15 41 5 below 15 41 4 2 Distinct User Classes SATTUBA may be used to output files for individual user classes using commands of the form SATTUBA network UC n which will output matrices of the form network ucn_t txt etc etc lf UC is used in the command line then the output matrices represent all the possible user classes with matrices of the form network uc1_t txt network uc2_t txt etc etc 15 41 4 3 Alternative Matrix Formats 15 41 5 5120257 Apr 15 Section 15 By default SATTUBA outputs matrices using TUBA format 1 CSV al
90. 1X allow the user to select data by reference to a Dirck Access Code as opposed io referring to say free flow travel time by name Dirck Access is a very egotistical pseudonym for Direct Access which it tries to replicate The precise details of Dirck Access files are not important here the most important point to appreciate is that each data field 15 46 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 21 2 15 21 3 5120257 Apr 15 Section 15 stored on a SATURN UF file has a code associated with it free flow travel time for example is coded as 1803 so that asking for free flow travel time to be annotated in P1X causes the program to read and annotate record 1803 The same effect can be obtained by referring to 1803 directly Note that the final digit in a DA code indicates what type of data is stored Thus all integer variables are stored in codes ending with a 4 whereas all real numerical data i e numbers which may include a decimal place such as free flow travel time above end with a 3 e g 1803 Post 10 7 real arrays may also end with an 8 and eventually integer arrays with a 9 A second point to note is that the coded data arrays refer to either a simulation links b simulation turns or c assignment network links which include both a and b plus all buffer links so certain DA codes will not be relevant under certain circumstances T
91. 7 Apr 15 15 124 Section 15 SATURN MANUAL V11 3 Special Options and Facilities a SATSTAT Module q Main Option __ Network File EPSOM9BAXX UFS Optional Additional UF Files VONELUCLUT daH Moly Network File 2 EPSOMSBRXX UFS J Network File 3 We now run SATSTAT and the module will now for each network in turn Run SATLOOK and SATDB to determine the version of SATURN in use Run SATLOOK and SATDB to extract the summary statistics and Run the SATSTAT Fortran program to generate a summary statistics file in CSV format The output s from the process will be a one or more CSV files with the same filename as the network UFS file In our example the two output files will be EPSOM98AXX CSV and EPSOM98RXX CSV 15 49 2 2 Using the SATSTAT Spreadsheet Once the Summary CSV files have been produced we may import them into the SATSTAT spreadsheet the latest versionof which at the time of writing is called Summary Report Excel2007 v4 10 xlsm The process has however not changed since the following example which refers to Summary Report v3 00 xIs as shown below was created The spreadsheet consists of a number of worksheets A Version Control worksheet for reference only ASummary worksheet this is the main report and Anumber of imported CSV summary files 5120257 Apr 15 15 125 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities EJ
92. 73719 51 1367360 0 3 2 449214 154 3921 0 006764 0 099412 0 209461 96 67 0 007531 0 000661 O 007697 96 87 73716 99 1363020 0 3 2 21613 99 01255 i 0 00891 0 109396 0 219731 97 66 0 005951 0 000571 0 007384 99 46 73716 19 1362522 0 3 1 23834 51 6912 0 004953 0 0769 0 179347 99 52 0 005552 0 000521 0 005915 99 58 73715 76 1363704 0 3 1 05451 38 60629 0 004379 0 059696 0 106201 99 57 0 00429 0 000391 0 004261 99 93 73715 17 1362662 ODO ON OH A WN yea ea File Edit Search Project View Format Column Macro Advanced Window Help D6 68 9 88 08 3 8 B 2B rem 10 T 20 ab 0 Iteration Percentage Gap 266 1230 70 6745 23 6462 9 2933 4 4406 2 2026 2 pete wae ots PO o2591 4435 2254 esa SE O959 O740 O566 O461 Oo 2d mh A w Mm He 5120257 Apr 15 15 156 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities EXAMPLE OF THE XCP FILE C UltraEdit 32 E WWetwork XCP E File Edit Search Project wiew Format Column Macro Advanced Window Help NS6SE SAR B 2a EmTe zi Network acP _ 1 EF IRAM SE a E A T O a S a a S a A ccc 2 KONSTP 3 3TPGAP 4 ISTOF 5 6 MET SAVEIT UNCRTS 2 NISTOP 3 MASL 10 NITA 3 11 END 15 55 QUIET amp QUICK Options via SATWIN The QUIET and QUICK options in SATURN see section 14 9 and 14 10 may also be activated via SATWIN10 or SATWIN11 Once QUICK an
93. ATALL the performance benefits will vary between models and the PC hardware available The splitting of the production of the PIJA into zones blocks is currently undertaken based on the sequential zone numbers and the distribution of trips in the matrix is unlikely to be equally shared between the blocks of zones In addition for each of the SATPIJA runs the network matrix and control files need to be copied to from the production folders which will incur a performance hit The performance of the distributed SATPIJA_ MC on a very large SATURN network is shown below in Figure 15 10 As noted above the potential benefits will be dependent on the model and PC hardware used 15 146 SATURN MANUAL V11 3 SATURN Special Options and Facilities Figure 15 10 SATPIJA_MC Performance Very Large Network E CPU Ratio A tn _ lt 9 z _ c a cD Sem O UO a eTe S N eTe c pm a x LLJ t e X 1Core 2Cores 3Cores 4C ores 5Cores 6Cores 7Cores 8 Cores 15 53 3 5 Performance Scaling As illustrated in the figures above the practical testing showed that there were typically negligible performance benefits over and above the use of five cores This throttling of the performance arises due to the limited memory available within the internal CPU Level 1 2 3 caches Conversely practical testing on other hardware systems such as Blade servers shows further performance benefits ari
94. ATURN input data conventions see for example 6 10 with node numbers in fixed columns followed by a single link flow or both node numbers and flow may be input totally as free format or CSV by setting a parameter PLODFF T in the network OPTION data segment see 6 1 By default PLODFF F Note that pre loaded links should normally include both roads and turns in a simulation network Including only roads will lead to discontinuities in flows at simulation junctions Within free format text files PLODFF T a further 8OPTION parameter PLFF3 T requires that each input record contains 4 fields A B C and flow Thus links are distinguished from turns by always including an explicit third C node field which is equal to zero for a link and the turn C node otherwise i e A B 0 link flow A B as opposed to A B C turn flow A B C Alternatively if PLFF3 F then link records require 3 fields A and B followed by the flow whereas turn records require 4 fields in total A B C and flow By default PLFF3 F For fixed column input PLODFF F PLFF3 does not apply since the fixed data columns used for a C node will simply be blank or zero for a link and the flow data is in the same fixed columns for both links and turns See Section 9 12 3 for suggestions as to how the pre load facility may be used in combination with the parameter ZILCH to carry out a 100 pre load Pre Loading Bus PCU Flows
95. B The travel times associated with bus routes are normally calculated by summing the standard link and or turn times associated with other vehicles along the route However it is possible to supplement these times to represent the additional effects of e g bus dwell times at stops or bus speeds being slower than cars The extra time may be introduced using either i an additional time proportional to the total distance over the whole route li explicit link by link extra travel times coded as knobs In both cases the additional travel times are calculated once and for all per route when the network is built within SATNET and then recorded within the uf files This means for example that it is not possible to view the extra travel times per link using the bus joy ride display within P1X The extra times are reported both within the individual route statistics and in the more aggregate statistics under option 6 in SATLOOK but not N B in the total pcu hrs etc reported under either options 4 or 5 in SATLOOK Under i the proportionality between extra i e stop time and distance in km is set by the parameter BUSSPK Bus Stop Seconds Per Kilometre defined within the amp PARAM namelist records in the network dat file In the event of there being more than one bus company BUSSPK may be subscripted so that e g BUSSPK 8 0 04 would set the specific value for bus company 3 Under ii link data must
96. H 1 2 FLPPS 0 016 FLPSS 0 005 These parameters were all chosen as appropriate figures for an average British car in 1981 More details may be found in Ferreira The role of comprehensive 15 84 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 33 5120257 Apr 15 Section 15 traffic management in energy conservation PTRC Summer Annual Meeting July 1981 Clearly these figures are now out of date and take no account for example of the breakdown of the flow into various vehicle types The parameters may be user set as standard namelist parameters within SATNET Determining Emission Statistics Emissions of harmful pollutants from road traffic are an increasingly important issue for engineers planners and politicians alike not to mention the general public who have to live in it It is also an extremely complicated process both in terms of actual emissions e g variations between vehicles and their ultimate dispersion and chemical reactions Predicting emissions is as with fuel consumption 15 32 probably best handled post processing i e users will have their own particular favourite model or formulae for calculating emissions which will require both data from SATURN such as flows and or speeds and exogenous data such as meteorological data In such cases the best option is to dump the required SATURN data into say a link based text file using SATDB and to pass that data i
97. I the user needs to define the convergence strategy that describes how the SATURN convergence parameters should change in response to improving convergence in the trip matrices As shown earlier in Figure 15 12 the convergence parameters adopted for the early loops should be relaxed and progressively tightened as the demand model convergence improves lf the assignment convergence strategy is too relaxed then the supply demand model may not converge whereas setting too tight convergence criteria for the initial loops may over converge the highway assignment and waste CPU time As such it is a balancing act but it s better to err on the side of caution and over converge the assignment as a fully converged model remains the ultimate goal Running SATURN CASSINI In normal operation the CASSINI program is usually called internally within SATNET and produces a supplementary ASCII data file containing eXtra Convergence Parameters XCP which propose new values for the relevant convergence parameters such as MASL etc etc SATNET then reads in this new XCP file before fully processing the main network data file the parameters in the XCP file overwriting those contained in the network data file CASSINI is activated in SATNET by setting the parameter CASINI T under amp OPTION File Inputs CASSINI requires three input files namely 15 152 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities An existing SATURN Netw
98. IT T MASL 20 GAPYALUE 10 STPGAP 2 00 UNCRTS 1 00 NISTOP 1 NITA 5525 SAVEIT T MASL 25 GAPYALUE 55 STPGAP 1 00 UNCRTS 1 00 NISTOP 1 NITA S 25 SAVEIT T M amp asbL 30 GAPYALUE 44 STPGAP 0 75 UNCRTS 0 75 NISTOP 1 NITA 550 SAVEIT T MASL 35 GAPYALUE 35 STPGAP 0 50 UNCRTS 0 50 NISTOP 1 NITA_S 50 SAVEIT T MASL 40 GAPYALUE 2 STPGAP 0 25 UNCRTS 0 25 NISTOP 1 NITA 3599 SAVEIT T MASL 45 GAPYALUE 14 STPGAP 0 20 UNCRTS 0 20 NISTOP 2 NITA 5599 SAVEIT T MASL 50 GAPYALUE 0 53 STPGAP 0 15 UNCRTS 0 15 NISTOP 2 NITA 55250 SAVEIT T MASL 60 GAPYALUE 0 254 STPGAP 0 10 UNCRTS 0 10 NISTOP 2 NITA S 250 SAVEIT T MASL Y0 GAPYALUE 0 004 STPGAP 0 10 UNCRTS 0 10 NISTOP 2 NITA 5 250 SAVEIT T MAsL s0 LOOPTHRESHOLD 99999 GAPYALUE 999 STPGAP 420 00 UNCRTS 10 00 NISTOP 1 MITA 5 25 SAVEIT T NASL 20 GAPVALUE 1004 STPGAP 15 00 UNCRTS 5 00 NISTOP 1 MITA 5525 SAVEIT T MASL 20 GAPYALUE 20 STPGAP 10 00 UNCRTS 5 00 NISTOP 1 NITA S 25 SAVEIT T MASL 20 GAPVALUE 10 STPGAP 2 00 UNCRTS 1 00 NISTOP 1 NITA S 25 SAVEIT T MASL 25 GAPYALUE 54 STPGAP 1 00 UNCRTS 1 00 NISTOP 1 MITA 525 SAVEIT T MASL 30 SAPYVALUE 43 STPGAP 0 75 UNCRTS 0 75 NISTOP 1 NITA S 50 SAVEIT T MASL 35 GAPVALUE 33 PTPGAP 0 50 UNCRTS 0 50 NISTOP 1 NITA S 50 SAVEIT T M amp sL 40 GAPVALUE 23 PTPGAP 0 25 UNCRTS 0 25 NISTOP 1 NITA 5599 SAVEIT T MASL 45 GAPVALUE 15 STPGAP 0 20 UNCRTS 0 20 NISTOP 2 NITA S 99 SAVEIT
99. L whereas UPDATE is applied in SATNET It is also under path based or OBA assignment MET 1 or 2 equivalent to WSTART T i e the first assignment uses the paths from the previous assignment as a perturbation assignment see 21 3 The distinction between a normal run and a re start is that the former must start with the network build program SATNET before commencing the assignment simulation loops see Figure 3 1 whereas the latter uses a previous network and starts with the assignment directly Subsequent assignment simulation loops are the same thereafter The first assignment requires in effect as input The final UFS file from the previous sequence This file contains the necessary network specifications and parameters The latest trio matrix UFM file The command SATALL network tripod RESTART carries out a full simulation assignment loop but taking its input from the previously converged file network ufs as opposed to network ufn which comes direct from SATNET Note that it is the presence of RESTART on the command line which initiates the re start sequence i e no parameters within a dat or control file need to be set However an alternative DIY method to set up re start would be to copy a ufs file into a ufn file yourself and create a control file for SATALL with the parameter REGO T see 7 13 2 Not recommended The output version of network ufs will over write the original input version and w
100. LIMAX T the penalty would be initially set to 6 seconds but if at the end of the first assignment the flow on that link were sufficient to reduce the car speeds to 110 kph the new HGV penalty would be 1 100 1 110 3 27 seconds If car speeds dropped to less than 100 kph the HGV penalty would go to zero By introducing an interaction between two different sets of costs and flows on the same link in the same way that the delays to minor arm flows at a T junction are affected by and interact with flows on the major arm an extra complication is introduced into the assignment simulation loops which in principle could lead to non convergence and or multiple equilibria However compared to the interactions that go on within the normal simulation process the sort of 15 120 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 47 3 1 15 47 4 15 48 5120257 Apr 15 Section 15 interactions we are talking about here are relatively weak and touch wood should not lead to any extra convergence problems Statistics to demonstrate the degree of convergence e g the ratio of the total absolute changes in penalties to the total penalties are printed each time the adjustments are made and should converge to near zero Defining CLIMAX CLIMAX is a Logical variable set in the network dat files under amp PARAM which is set by individual user classes Thus CLIMAX 3 T turns on the CLIMAX option f
101. Microsoft Excel Summary Report v3 00 xIs Ba File Edit wiew Insert Format Tools Data Window Help TERA BENNE eee ae eer REN ae OREA ES TESES E ee Arial O a0 BU Be Se yy to n jE E E11 fe aa 6 ce HA0002 SATURN Support Import CSV Wright Atkins mp EPSOMSOAXA COM EPSOMSGRAS CON 12 11 oP lows 94 5 95 1 FolSAP 0 302 0 333 Le Ce e Statistics Summary Results EPSOMSSBAAA STA EPSOMSSR AA STA Matrix totals pcus hr 5013 1 5170 Transient Queues Total pcusl 39 5 156 3 lt Proportion carried over gt 0 5 3 0 CverGanachy Queues focus 1 4 09 5 Proportion carried over 0 0 5 6 Link Graise Times Total cu hra Ilga alee lt Proportion carried over gt 0 1 1 4 Tota Travel Times Total pou hra 155 4 503 6 lt Proportion carried over gt 0 2 3 3 Travel Distance Total peu krna 5230 1 oue yf lt Proportion carried over gt 0 1 1 3 Average Speed Overall Krah 33 16 lt Ratio gt 32 4 41 3 Delay Total peu hrs 40 9 205 9 Delay Vehicle mins veh 0 45 3 32 Congestion Index mins veh km 1 52 2 5 Average Trip Length km 1 04 1 56 Simulation Queues pcu h Ave Queue DA1433 39 36 158 16 ueue at End 081463 5 45 163 7 Turn Penalties focu frs hr not found not found Turn Penalties fnumberl not found not found Lele GL 15 49 2 3 Importing CSV Files To import our new Sum
102. N MANUAL V1 1 3 SATURN Special Options and Facilities 15 27 15 27 1 15 27 2 5120257 Apr 15 Section 15 N B An arboretum is essentially a Frank Wolfe algorithm based construct for which there is no direct equivalent under OBA Note as well that forests and arboreta can only be constructed IF the SAVEIT option is in effect see Section 15 23 Skimming Trees and or Forests Minimum Cost Trees and Matrices Trees 15 26 represent the full set of minimum cost O D paths where cost Is some criteria such as time distance monetary cost or most often generalised cost i e a weighted combination of two or more components such as time and distance which the individual O D paths or routes minimise They are called trees since if you plot the set of minimum cost paths from one origin to all destinations the resulting sub network resembles a tree which continuously branches outwards from its root origin such that there is only one possible path to each destination D The cost along the single path to D is therefore the minimum cost to D and a tree is therefore synonymous with minimum cost O D path Clearly trees depend on how cost is defined the path that minimises time between O and D is not necessarily the same path that minimises distance nor the one that minimises generalised cost Note that in the vast majority of transport models cost is synonymous with generalised cost
103. OMSSAX A STA EPSOMBRAS FRPSOMISGRAA STA rr cC ee ee eee Import CoV 11 90 1 Uaa Whilst Table 1 will remain unchanged Table 2 below will now report on the Differences and Differences in the summary statistics ie this network MINUS the one with the column ID just selected as shown below EJ Microsoft Excel Summary Report v3 00 xls ie File Edit View Insert Format Tools Data Window Help D oZ id a 7 e 1 F Al ZI ty a 100 10 k B Z UJ Z amp a y f A lt 0 00 c gt so 35 2 5048181 SATURN Support lJWright Atkins Date Created 15 03 07 Import CSW Version 3 00 Turn Penalties number not found not found Statistics Summary Results Matrix totals pcus hr Transient Queues Total pcus lt Proportion carried over gt Over Capacity Queues pcus lt Proportion carried over gt Link Cruise Times Total pcu hrs lt Proportion carried over gt Total Travel Times Total pcu hrs lt Proportion carried over gt Travel Distance Total pcu kms lt Proportion carried over gt Average Speed Overall kin h lt Ratio gt Delay Total pcu hrs Delay Vehicle mins veh Congestion Index mins veh km Average Trip Length Simulation Queues pcu h Ave Queue DA1433 Queue at End DA1483 156 9 3 1 156 8 397 0 483 5 88 1 6292 9 0 1 lt gt 0 100 2 65 3 O 1519 2 345 2 217 9 0 1629 9 2847 6
104. OOK Performance Medium Size Network using SKIM_ALL 15 53 3 3 15 53 3 4 5120257 Apr 15 Section 15 ma CPU Ratio lt 9 z _ c a oD Sem O Q eTe S N eTe c pm Ka x LLJ ea O xX 1Core 2 Cores 3Cores 4Cores 5Cores 6Cores 7Cores 8 amp 8 Cores SATUFO Multi threaded SATUFO Multi Core may be used to create a network UFO file from a UFC file see 15 23 7 The same implementation is used as with SATALL and SATLOOK skimming The UFO file may be created as part of the main SATALL assignment by setting SAVUFO T and MULTIC T or alternatively as separate standalone process following the main assignment via the batch file SATUFO BAT with MULTIC T previously used in the main assignment SATPIJA_MC Distributed Unlike the SATALL SATLOOK and SATUFO Multi Core applications SATPIJA uses a distributed approach whereby the creation of the PIJA file from the assignment is split into N blocks of zones see 13 4 9 with each block undertaken by a separate run of SATPIJA Each SATPIJA run is undertaken in a separate sub directory or production folder and an extra short SATPIJA run is undertaken at the end to combine the N smaller PIJA files into a single file The process is automatically controlled by a new SATPIJA_MC batch file 13 6 3 so in theory there are no changes to either the basic program SATPIJA EXE or to its associated batch file SATPIJA BAT 13 6 2 As with S
105. SATURN MANUAL V1 1 3 Special Options and Facilities 15 15 1 15 1 1 5120257 Apr 15 Section 15 SATURN Special Options and Facilities INTRODUCTION This section contains a series of notes on special features of SATURN and is intended to explain their use and or interpretation rather than to describe the nitty gritty of how for example to set up input files Network Aggregation and Simplification within Intermediate Bands N B This section first created in September 2011 replaces a previous section on How Tutorials which are no longer available General Principles of Network Simplification and or Aggregation SATURN networks are very often constructed in the shape of a doughnut see below where the area of most interest in terms of scheme testing is at or near the heart of the doughnut and the centre of the doughnut is coded as a simulation network with the outside made up of a buffer network See Section 2 3 Typical Schematic Diagram of SATURN Network Types Core Simulation Area Peripheral Simulation Area Buffer Area The justification for using the less precise buffer network description is that if one is interested in analysing schemes at the centre of the network the resulting impacts within the distant buffer network will be minimal and the extra time and effort required to code and run the full network as simulation cannot be justified A further advantage of a buffer network vis
106. SATURN on the basis of minimum time trees but then look at minimum distance trees Distance KNOBS data and tolls are by definition fixed However time may be defined in a number of different ways e g with or without penalties added and calculated at different points during the programs as elaborated below in 15 24 2 15 24 3 and 15 24 4 Note that these discussions refer equally to time skims as discussed in 15 27 Travel Time Alternative Definitions Time unless otherwise qualified refers to the time to traverse a particular assignment link by a standard vehicle or pcu However in certain situations it may be necessary to consider differential times by say user class or by bus lane These are explained further below 15 24 4 For display purposes e g in P1X time is very often sub divided into various sub components e g fixed times transient delays queuing delays etc etc Equally link travel times as displayed may or may not include additional delays associated with one or all of the delays from turning movements at the downstream end of the link Calculating Times at Different Stages within SATURN Link travel times are set at 4 different stages within SATURN as follows Free flow travel time NO Times calculated at each assignment iteration 3 Travel time as calculated at the end of the assignment 4 Travel time as calculated for simulation turns only by the simulation Of these 1
107. See 7 11 12 15 53 1 2 Numerical Differences between Multi Core and Standard Programs 15 53 2 5120257 Apr 15 Section 15 The development work required the computational intensive sub routines to be modified so that they may be undertaken in parallel The work also required the modified source code to be created separately using a different software compiler than the standard release specifically Intel Virtual Fortran rather than Salford An unavoidable consequence of using a different compiler is the introduction of very small differences in the numerical precision that the internal calculations within the assignment are stored in their respective versions The differences should generally be too small to spot but there may be some cases where like the analogy of a butterfly flapping its wings the two may give detectable even significant differences although each will be perfectly valid solutions Consequently the results from the SATALL MC executable may be different from the standard version However the other executables that undertake the secondary analysis should not be affected as they are either i only re building the existing stored paths rather than undertaking new assignments ii undertaking the analysis for each user class in parallel using the same process Processors Cores and Threads Processors or Central Processor Units CPUs to give them their full name provide the computing power for the Persona
108. T MASL 50 GAPVALUE 0 54 STPGAP 0 15 UNCRTS 0 15 NISTOP 2 NITA 5 250 SAVEIT T MAsSL 60 GAPVALUE 0 254 STPGAP 0 10 UNCRTS 0 10 NISTOP 2 NITA_s 250 SAVEIT T MASL 70 GAPYALUE 0 004 STPGAP 0 10 UNCRTS 0 10 NISTOP 2 MITA 35250 SAVEIT T MASL 50 GAPYALUE TERMINATE STPGAP 0 10 UNCRTS 0 10 NISTOP 1 NITA S250 SAVEIT T MASL 60 5120257 Apr 15 Section 15 15 155 SATURN MANUAL V11 3 SATURN Special Options and Facilities EXAMPLE OF THE DIADEM DEMAND MODEL FILE EJ Microsoft Excel 4 4C_results csv aay Edit view Insert G Type a question for help Step lengtl Max flow c Obj fn Gap Cost stability Flow stability Abs Rel RAAD AAD RMS 5 RAAD AAD RMS 5 Trips Cost 0 3 0 3289 929 106751 3 0 0 D 0 D 0 0 0 73792 98 1333444 0 3 5 3062 4400 637 124263 5 0 083895 1 1828 1 906136 50 62 0 040416 0 003911 0 034085 70 69 73760 62 1405156 0 3 10 6656 1904 122 84682 3 0 033067 0 414765 0 759361 62 44 0 039986 0 003704 0 039421 72 02 73754 44 1390225 0 3 5 5305 624 1756 55114 65 j 0 052882 0 423689 0 664608 62 90 0 029493 0 00266 0 025931 60 76 73737 05 1371159 0 3 2 666963 693 2769 40291 45 0 022827 0 306729 0 592542 89 12 0 019947 0 001641 0 01706 90 04 73730 31 1375486 0 3 4 777853 328 427 31538 26 0 015312 0 234167 0 480673 93 24 0 014037 0 001346 0 015647 95 60 73722 41 1366421 0 3 1 71161 176 5888 0 009991 0 143058 0 292256 97 21 0 011124 0 001056 0 010769 97 10
109. URN Special Options and Facilities 15 34 5120257 Apr 15 Section 15 calibrated coefficients will undoubtedly follow and users are strongly encouraged to put forward their own models Default parameter values for four of the pollutants excluding CO have been extracted with some fairly broad brush assumptions e g that a primary stop involves a deceleration from 50 kph to rest and the reverse acceleration from the data used in the 1988 Leeds PhD dissertation of Athanasios Matzoros see also A Model of Air Pollution from Road Traffic and Il A Matzoros and D Van Vliet Transportation Research pp 315 335 Vol 26A 1992 Default values are listed below Grams PCU Kilometres Cruise Idling Primary Secondary Hour Hour Stop Stop Carbon dioxide 70 0 0 00 1200 00 16 000 5 000 Carbon monoxide 0 0 304 80 180 00 2 22 0 444 Nitrogen oxides 0 0 102 60 1 80 0 42 0 084 Hydrocarbons 0 0 57 00 30 00 0 39 0 078 Lead 0 0 0 36 0 09 0 0024 0 0005 Carbon dioxide parameters are extracted from the fuel consumption parameters on the assumption that most fuel is converted into carbon dioxide Parameter values may be reset by users using the namelist inputs to SATNET within a network dat file See Section 6 3 3 all parameters are reals Their names are constructed using the following conventions All names commence with the characters CO CO2 XNO HC or PB The next character is a P for per The final chara
110. a separate file referenced by INCLUDE Note that fields ii and iv must be integers as well as clearly being valid numbers but the speed ili may be input as a real value Normal logic checks Note if DUTCHST has been set to permit longer node numbers the matching columns will be 21 25 and 53 55 respectively 5120257 Apr 15 Section 15 15 119 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities that e g CLICKS speeds are less than normal speeds etc etc are carried out and error messages produced as necessary The V records will be ignored in the same way that default soeed flow curves by Capacity index with a D in column 1 are ignored when the buffer network is built Note as well that if any V records are included under 33333 and KLUNK 1 then any reference to FILVSD is ignored you cannot therefore use both methods to define KLUNK 1 data at the same time 15 47 2 4 KLUNK 2 Disaggregate by Link 15 47 3 5120257 Apr 15 Section 15 Not yet implemented This will probably be done in conjunction with the 33333 input formats above but per link rather than per capacity index Thus the HGV Say speed flow curves will be defined independently per link e g as a flat maximum speed until it intersects with the normal speed flow curves Fixed Maximum Speeds CLIMAX An alternative to having a fixed difference in travel times per user vehicle class is to specify a fixed maximum speed
111. al SSATPIJA_MC EXE datasets into a single file The management of the process is undertaken automatically by the software See 15 53 3 3 New Multi distributed as per Final SATCH MC BAT v10 9 24 SATPIJA with each user class SATCH_MC Release and onwards undertaken on a separate SATCH_MC EXE thread See 15 53 3 6 Secondary See SATUFO l l Analysis above Undertaken using UFO files 15 53 1 1 SATALL Multi Core Restrictions SATPIJA_MC We note that the multi core facilities within SATALL do not yet work with every possible combination of assignment options Thus it does not work with any form of elastic assignment with stochastic assignment SUZIE T or with networks which incorporate Motorway Weaving Segments Section 15 40 If 5120257 Apr 15 15 142 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities there is sufficient demand to include such options it will be considered for future inclusion SATALL also does not work with either path based or origin based OBA assignment because the theoretical principles of these algorithms require them to be undertaken in a purely sequential process In addition multi core requires that there is sufficient RAM provided to store the full trip matrix in core with certain matrices it may therefore be necessary to set a control parameter SPARSE F to select a more efficient system for matrices where more than 50 of the Tij cell values are positive
112. alternative though less rigorous approach would be to distinguish between probable and improbable links where an improbable link A B is very unlikely given its cost and the alternatives from A to B to be part of any min cost trees but an exact assessment might take longer than the time saved by eliminating that link Eliminating improbable links will speed up individual Frank Wolfe iterations 15 173 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 57 15 57 1 15 57 2 5120257 Apr 15 Section 15 but it would be necessary near the end of the process to re introduce all links just to confirm that none of the improbable links should be reclassified As long as Frank Wolfe finds lower cost auxiliary solutions on each iteration it should not matter if it finds the absolute minimum cost auxiliary as long as no potential paths are being ignored in perpetuity The above thoughts on eliminating certain links are based on the empirical observation that in most spider web networks less than 50 of all aggregate links are assigned flows so that had they been eliminated a priori the ultimate solution would be the same but achieved more quickly Several good topics for further research Residual Incorrect Path Flows and Restricted Frank Wolfe Algorithms Residual Path Flows Definition A problem in identifying path flows under the Frank Wolfe algorithm for solving Wardrop Equilibrium which does
113. alues In almost all cases the two give virtually equal answers but there are odd examples when one result appears to be unreliable and we prefer to believe the lower values Turns at simulation dummy nodes experience zero delay by definition and therefore zero marginal costs They are included in the output mec files with values of zero Similarly bus only links and or turns are assigned zero MECC values 15 135 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 50 7 15 50 8 5120257 Apr 15 Section 15 Marginal Costs on Links In addition to calculating marginal costs on simulation turns SATMECC also calculates marginal costs for pure links i e roads A B as opposed to turns A B C which are a in the buffer network or b simulation links with capacity restraint speed flow curves In both cases it is only necessary to use equations 7 47a and or 7 47b Note that simulation links which do not have speed flow curves are excluded Links are included within the output mec file See 15 50 7 and are identified by a value of O in the third node field i e A B 0 as opposed to A B C for simulation turns Simulation links without capacity restraint soeed flow curves are totally excluded as are all centroid connectors The SATMECC Batch Control File A special batch file SATMECC bat has been set up in order to carry out the calculations detailed above making use of the program SATLOOK Its specific
114. andard set of default parameter values are adopted Note that a slightly different way to customise the set up of an interactive program is to use the break option in a key file see 14 5 5 whereby the necessary commands are contained in the key file which initiates the run but terminates on break allowing the user to carry on as per normal from that point Network Updates The Update Option It is very often the case in calibrating a network that successive test networks differ only marginally from previous tests It is possible to take advantage of this fact by using the output from former runs to provide a realistic starting point for the subsequent run More specifically values of the previous flow delay parameters including values of the ratios of actual to demand flows QRF see 17 2 are extracted by SATNET from an update network to set initial values for input to the first assignment rather than starting cold with not very realistic default values This has the great advantage of potentially significantly reducing the number of simulation assignment iterations on the second run by making the initial assignment far more realistic In addition post 10 8 selected data relating to the simulation is also extracted from the update network rather than setting default values in order to make the first simulation more realistic In order to invoke the UPDATE option two steps need to be taken Set UPDATE
115. ar network but which may be used either in different forms of networks e g simulation networks use arrays that do not appear in buffer only networks or in future versions of SATURN At the present moment array codes in the range 3003 to 3293 are never used and will not barring acts of God etc etc be used in the future they are therefore recommended as being exclusively reserved for use by users Extended Dirck Access Codes In SATURN versions 8 5 and beyond the coding conventions used to identify Dirck Access arrays were extended to cope specifically with the problems created by more than 10 user classes where in effect all available numerical 15 47 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 21 4 15 22 5120257 Apr 15 Section 15 codes were used up Thus class specific flows were stored in arrays 3803 3813 3823 etc for user classes 1 2 3 etc up to 3893 for user class 10 3903 however was reserved for something else so that an 11th user class could not be accommodated The solution adopted was to add class specific digits BEFORE the basic code so that with 11 classes the DA flow codes became 3803 103803 203803 etc up to 1103803 The effect was similar to having decimal codes such as 3803 0 3803 1 3803 2 but retained the basic principle of integer codes At the moment such codes are used in networks with more than 10 user classes in UFT files to store data from m
116. are defined by integer seconds as opposed to being continuous variables Again this implies that the solutions are not true global optima but equally means that they may be insensitive to small changes in junction parameters e g flows and therefore they converge more rapidly Using SIGOPT and or SATOFF within SATALL As an alternative to optimising stage green times outside the assignment simulation loop as discussed in 15 31 2 it is also possible to do so within the loop using SATALL Thus setting the parameter SIGOPT TRUE in preferably the original network dat file or in the SATALL control file results in a two pass simulation process within the standard loop Thus on the first pass the simulation uses the current stage green times and the latest assigned flows it then updates all stage times at signalised junctions independently and re runs the simulation in a second pass Statistics describing the degree of changes to the green times appear both on the screen and in greater detail in the LPT file Note that the option SIGOPT automatically optimises all nodes there is as yet no option to optimise over a subset of signals although this can be done using the batch procedure SIGOPT described in 15 31 6 below Equally the offsets can be automatically optimised within each simulation by setting SATOFF T or offset optimisation could be done on its own by setting SIGOPT F and SATOFF T but see below this i
117. are not provided nor are they necessary for users An updated version of any preferences file may be produced by the program via the files sub menu and these will contain both the input values plus the new values of any parameters changed by the user in that session Hence users can customise a preferences file to their own individual specifications and any subsequent program runs will use these specifications Preferences files exist for the following programs P1X SATED SATDB MX and SATLOOK 15 6 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 3 5120257 Apr 15 Section 15 By default preferences files are stored in a specific sub directory set by SATIOKEY DAT see Appendix Y but it is possible to select alternative preference files using the PREF keyword in standard bat files For example PIX network PREF C DVV PREFS JIMBO selects the preferences file JIMBO DAT in subdirectory DVV PREFS rather than the default P1X0 DAT In certain cases variables which can be namelist set in SAT1OKEY DAT may be over written by individual Preferences Files e g GO4IT and KPEXT In general the values set in SAT1OKEY DAT might be thought to refer to values for an organisation as a whole while values set in Preferences Files might be more appropriate to individual users or jobs If however a program cannot locate a preferences file it is not the end of the earth or the program In that case a st
118. assuming of course that there are alternative routes available Banned turns may be introduced by coding them as bus only turns even if there are no buses the model response to a bus only turn is to prevent any elements in the trip matrix in this case lorries from using those turns Some caution must be exercised when using PLOD so that other forms of fixed vehicles are not loaded twice For example bus routes should not be coded as part of the lorry network only as part of the normal network since any bus flows in the lorry network will be automatically added as fixed flows to the normal network Clearly the same basic procedure is carried out with any combination of assigned vehicles not necessarily just lorries and cars Pre loading Distance Minimisers Another useful application of the PLOD option is to carry out a separate assignment of a trip matrix of distance minimisers whose route choice is by definition independent of other trips How of course one defines such a trip matrix in the first place is entirely up to the user Again distance minimisers may be treated as a separate user class It is also quite feasible to do several stages of pre loading For example you can start with the distance minimisers pre load them onto a lorry network in which case the output flows would consist of both lorries and distance minimisers and then pre load that network onto a normal network Clearly some care is called for he
119. ately per individual link The choice is set by an Integer input parameter KLUNK defined under PARAM Thus if KLUNK 0 the default CLICKS u applies to all links for user class u If KLUNK 1 then in effect CLICKS becomes a two dimensional array such that CLICKS v k defines the value of CLICKS for vehicle class v for all links with capacity index k If KLUNK 2 then every individual link can potentially have its own unique set of CLICKS values N B With KLUNK gt 0 the values of CLICKS are defined by vehicle class not user class but recall from section 5 8 that each user class should be associated with a particular vehicle class as set on the network 88888 data records so the general principle that each user class has a maximum speed per link is retained The reason for using vehicle classes directly rather than user classes is that there are generally a much smaller number of vehicle classes e g cars light and heavy lorries and it is really the type of vehicle that determines maximum speeds not whether a car driver chooses a route based on minimum time or distance It also allows users to introduce new definitions of user classes but with the same set of vehicle classes e g split a user class Work into HB Work and NHB Work but both are part of Vehicle Class 1 without having to update CLICKS Plus it allows data files such as FILVSD files see below to apply to more than one network as long as both networks use the sa
120. ation is as follows Call SATMECC network UC n KR control Files network ufs Input network file Network mec Output ascii file of MECC values Network LPL Output line printer file from SATLOOK Control dat Control file Optional UC n optional requests that the calculations be carried out for user class n and the output file will be network ucn mec UC requests a loop over all user classes to produce files network uc1 mec network uc2 mec etc etc Output mec files contain 8 fields formatted as follows Field 1 A node Field 2 B node Field 3 C node for a turn 0 for a link whether simulation or buffer Field 4 The base delay to turn A B C in seconds Field 5 The total MECC in seconds N B marginal time not cost Field 6 Own MECC Field 7 Arm MECC Field 8 Interactive MECC For pure links A B i e simulation or buffer links fields 7 and 8 are blank Note that Fields 1 2 and 3 all occupy 6 columns in order to improve legibility for networks which have up to 5 digit simulation node numbers This may cause 15 136 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 51 5120257 Apr 15 Section 15 problems in input to certain SATURN programs where the convention is to have 5 columns by default Note that the latest 10 8 version of SATDB allows either 5 or 6 column node fields under the input of miscellaneous text files lf DUTCH T and the maximum node number used i
121. ations 13 3 14 or SATCH matrix cordoning 12 1 12 In such cases the use of UFO files is generally strongly recommended as they are considerably faster than using UFC The choice of UFO vrs UFC is generally controlled by a namelist parameter USEUFO T or F respectively which may be set in either network dat files which sets the general default see 6 3 1 SATPIJA or SATCH control files 13 3 14 and 12 1 12 In addition the UFO format used for OBA 22 5 2 may also be adapted for use with link based Frank Wolfe assignments essentially the path flows in the UFC file are converted into the equivalent or strictly soeaking nearest equivalent acyclic flows which are then stored in a UFO format See 22 5 3 UFO files as explained in Section 22 5 have at least one major advantage over UFC files in that they enable warm start assignments to be used under all possible conditions In addition the same analysis application may run much faster with UFO than UFC files since any analysis of all O D routes with UFC contains a 15 56 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 23 7 peor ee loop over the number of iterations N which UFO avoids so that in principle it may be N times faster The downside of creating a UFO file is that if the Frank Wolfe solution is not particularly well converged and contains many examples of cyclical flows eliminating those cyclical flows may lead to a significantl
122. be more important If all signals in the network operate on the same cycle length then life is simple all junctions should be simulated using that cycle time and there is no need for any changes from the default LCY If however different signals operate on different cycle times then generally speaking LCY at signals should be set to the local cycle time Before considering non signals let us consider the effect of different cycle times lf A and B are adjacent junctions with equal values of LCY then the OUT cyclical flow profiles at A become the IN profile for link A B and any structure in the profiles is carried forward from A to B This enables the effect of signal co ordination between A and B to be modelled If on the other hand A and B were both signals but on different cycles it follows that at certain times they would be in phase and at other times out of phase Rather than trying to model the whole range of possibilities SATURN tries to model the average behaviour by assuming that if A and B have different values of LCY the A B IN profile is perfectly flat regardless of what the OUT profiles were like Clearly this is not a perfect modelling assumption but it has the definite advantage of being easy to implement Thus for non signalised junctions we recommend as a very general rule of thumb that LCY should be set equal to the value of the cycle time at the signalised junctions which most effects conditions at
123. benefits from using sub files For example if you have a large number of networks in a certain study all of which have the same co ordinates it is much simpler to update a single xy file than to update every single network file when you wish to make changes Clearly the resulting dat files use less disk space as well Sub files may also be created and or extended interactively using P1X see Section 11 9 2 6 and 11 9 2 7 Finally we note that it is possible and often highly desirable to have effectively the same data appearing in more than one file For example data for the same simulation node may appear in several locations such that one may deliberately take precedence over another as part of coding alternative scheme and or scenarios See Section 6 15 for advice on using FIFO TOPUP and DOUBLE options 15 77 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 31 15 31 1 5120257 Apr 15 Section 15 Setting Optimum Stage Green Times Background A common problem in setting up future year SATURN networks is to determine appropriate signal setting parameters The same problem does not arise with current networks since in theory at least the settings may be observed However the easy solution of carrying present day settings forward into the future is clearly fraught with errors since there is no guarantee that good settings for today s traffic levels will still be good in the fut
124. by skimming the forest For less than perfect convergence the inevitable norm the minimum costs will be potentially less than the costs along some assigned routes and therefore less than the average In certain respects assuming the inevitable less than perfect convergence the forest cost matrix is better than the minimum cost matrix since it corresponds to the costs actually incurred according to the assignment it might therefore be better to use within economic evaluation On the other hand it requires considerably more CPU time to calculate And strictly speaking neither is correct in the sense of being equal to the cost matrix which would be obtained under perfect convergence in general one would expect that the minimum cost matrix would be a slight under estimate of the true ultimate cost matrix and the average would be a slight over estimate Thus faced with two alternatives neither of which is correct but one of which is much cheaper to calculate there is a strong case to be made for choosing the cheaper alternative i e to take cost matrices as equal to the minimum cost matrices rather than the forest skims Note however that this advice does certainly not apply to any sub components of cost such as time or distance which can only be obtained reliably as skims over forests as opposed to say building a minimum time tree or skimming a minimum cost tree Finally there is a third method by which cost mat
125. ch contains certain fixed data such as the link distances The full COBA input file requires further information such as lit unlit which is not available from within a SATURN network file on its own Finally SATCOBA generates a set of turning proportions at each internal simulation junction the turning matrix in COBA terminology with a directionality flow factor for 2 way roads Thus the output from SATCOBA is a text file extension cba which contains four sections anetwork definition section COBA KEY 042 network flows KEY 056 network fixed data KEY 060 the turning matrix at each junction KEY 082 all in a format specified by COBA and which we need not specify in detail here To run SATCOBA which can effectively only be run via its bat file type SATCOBA netl net2 net3 KR control where net1 ufs net2 ufs net3 ufs are the output files from different time periods whose factored flows are to be optionally added together The output text file would be net1 cba A control file control dat which sets over writes various parameters may be optionally defined via the bat file If none is defined a nul default file satcoba0 dat is used which basically accepts all program defaults See 15 42 2 Like SATTUBA SATCOBA is very much work in progress comments on a postcard please to DVV The SATCOBA Control File The control file consists of a standard set of namelist paramet
126. cle class 3 The file is terminated either explicitly by 99999 in columns 1 to 5 or simply by the end of the file As with CLICKS 1 under KLUNK 0 we anticipate that CLICKS will not apply to the vehicle class cars generally 1 so that one of the input fields the first will be uniformly zero N B Note that the input maximum speeds are defined by vehicle class NOT by user class 15 47 2 3 Extra 33333 Data records To define the maximum speed for a particular combination of vehicle class and Capacity index the user must include a record in the network dat file similar to default speed flow records per capacity index 15 9 5 under 33333 see note 16 section 6 6 with 1 The character V in column 1 followed in free format by ii The vehicle class iii The maximum speed CLICKS in kph iv The capacity index Thus the 3 data fields following V may be in any columns as long as they are separated by either a blank or a comma However for visual reasons we would strongly recommend having the vehicle class in columns 2 5 the maximum speed in columns 11 15 and the capacity index in columns 43 45 as done in the latter two cases for default speed flow curves In fact it would make good sense to include any specific maximum speeds by vehicle class index immediately after the equivalent default speed flow record to make any comparisons of data much more transparent Alternatively they might be contained in
127. corresponds most closely to the true assigned paths generates fewer problems in terms of uniqueness reliability etc etc but not NO problems see points 6 7 and 8 below However it may take considerably more cpu see point 9 below The first true minimum distance etc has the advantage of being unambiguously defined but on the other hand it may not correspond to a route that would actually be used by drivers However it might be useful to compare a true minimum distance matrix to the actual distance matrix to see how near users are to minimum distance Equally skimming distance etc from a single minimum cost tree is highly unreliable see 15 27 2 However skimming a single tree may be much faster than skimming a forest and if only an approximate answer is required may be sufficient On the other hand if we are interested in a cost matrix for use say in an external demand or evaluation model where cost refers to the generalised cost used in the assignment then methods a and b above give identical results while c differs only in terms of non convergence Indeed if we have achieved perfect Wardrop Equilibrium cost should be equal on all routes used and c must give the same result as a and b In practice deviations occur due to a lack of perfect convergence so that a must give lower values than c The answer which would be obtained ultimately by a perfectly convergent Wardrop
128. cters are K for kilometre CH for cruise hour IH for idling hour PS for primary stop or SS for secondary stop Thus HCPCH is the variable denoting hydrocarbons emitted units of grams per hour cruise time per pcu Estimating Primary and Secondary Stops While the simulation element within SATURN does not explicitly model the exact progression of every vehicle as they move down a link it is possible to infer certain properties of their progression Thus SATURN estimates the number of times on each simulation link that vehicles execute primary and secondary stops The distinction between the two forms of stop is basically the following Imagine a minor arm at a priority junction with a stop sign at the end every vehicle approaching that junction should must come to a complete stand still either at the stop line if there is no queue or behind the last vehicle in the queue that is a primary stop If there is a queue and vehicles depart from the head of the queue one at a time then vehicles further back will move up by accelerating and then decelerating to a stationary position these are secondary stops 15 86 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 35 5120257 Apr 15 Section 15 Clearly this two way split does not exactly represent all possible vehicle movements in a queue but it may well be sufficiently good for estimating secondary parameters such as fuel consumption or emissions an
129. d Therefore it is not possible to use say the second set of link times in a new definition of generalised cost although there is probably very little reason why one should ever want to do that the important thing is to be able to re create the routes to which trips were assigned at each iteration 3 Atthe conclusion of the assignment times are also calculated using 5 1 with V equal to the final assigned flows These are therefore the best times as calculated by the assignment but somewhat perversely they are never used by the assignment to build routes These times should therefore be used to calculate the minimum cost routes at convergence e g to calculate an O D cost matrix for evaluation purposes N B Although routes calculated using the above times were not necessarily generated by the assignment this is not to say that they definitely were NOT Indeed in most cases the final routes will correspond to one and probably more than one of the routes actually generated so that they are not necessarily unrepresentative However some care should be exercised in their analysis 4 When the simulation stage is run after the assignment the delays on turns in the simulation network are re calculated by simulation If the model has converged properly these delays should differ by only a small amount from those calculated by the assignment and be identical in the event of perfect convergence These times are somewhat more realis
130. d SATURN format e g as for input counts section 6 10 where each record contains the _ link turn identification in fixed column formats in columns 1 15 1 30 under DUTCH followed by the knobs data for that link in essentially free format e g comma separated However post release 11 2 4 the data records in a KNOBS file may be entirely free format e g CSV by setting an amp PARAM parameter FREEKN T in the network dat file In this case the link turn numbers A B and or C do not need to be in fixed columns but free format Note that a third node C must always be explicitly included for links either as 0 or in the case of CSV by 15 14 5 2 KNOBS Data on Centroid Connectors 5120257 Apr 15 Section 15 There is an important distinction between data input internally under options i and ii above and externally under ili That is that the internal 33333 data may only be defined for road links whether in the simulation or buffer networks plus buffer simulation connectors whereas data input in an external file may also be defined for all components within the SATURN assignment networks e g turns oy including 3 nodes and simulation centroid connectors as well defined by including a C in columns 1 6 or 11 to identify the zone columns 1 11 or 21 under DUTCH Thus to define an outbound centroid connector from a zone Z to node A where A is either a buffer node or an external simulation node
131. d for providing a very broad description of the state of a junction The rules for estimating primary and secondary stops are like their definitions somewhat arbitrary Thus for minor arms at priority junctions all arriving traffic must make a primary stop if its turn is over capacity or if the queue per lane is greater than 2 If the queue per lane is in the limit zero the probability of a primary stop is equal to the calculated probability of there being no gap For queues per lane between 0 and 2 pcu s a linear relationship is assumed Secondary stops are calculated by assuming that all primary stops make a further number of secondary stops equal to the queue length per lane divided by the number of vehicles that can depart from the stop line in a platoon once a gap occurs assumed equal to one over the probability of a gap Roundabouts are treated in the same way as minor priority arms For major priority arms secondary stops are ignored and a primary stop only occurs if the arm is over capacity or if at the moment of arrival the expected queue length per lane is greater than 1 At signals all arrivals primary stop during a red phase or during the green phase if the expected queue is non zero Secondary stops occur whenever the lights go red to all vehicles in the queue at that instant Altered Data Formats in DAT Input Files Generally data input files to SATURN programs are formatted meaning that repeated numer
132. d more flexible and generally recommended in preference to PLOD see 7 3 However as discussed in 15 5 2 and beyond below a number of other possible applications have emerged over the years In simple terms pre loaded flows are fixed flows introduced onto the network before any assignment takes place but which contribute to the total flows used to calculate costs times in the assignment They are always defined in units of ocus hr and have no other properties such as being part of a particular user class or vehicle class However in terms of calculating their total pcu hrs etc it is assumed that their travel times are as defined for user class 1 Note that in certain circumstances pre loaded flows may contribute to exit and or entry flows on simulation links see 15 6 2 For example if a flow of 100 pcus hr is preloaded on turn A B C but no flow is preloaded onto link A B then a flow of 100 pcus hr must be added as a downstream entry flow on A B Pre loading HGV s The procedure to be followed with heavies plus cars would be to Set up a heavies network and carry out a full SATURN run assigning only a matrix of heavy vehicles Set up the normal network with the previous demand i e not actual flows pre loaded onto the network and treated as fixed flows in the same way that buses are The second or normal network file would have PLOD T in amp OPTION and preferably the name of the pre loaded fil
133. d on NITA_S 30 independent of the value in net ufs If a numerical parameter is not used NITA_S is simply taken from net ufs In fact SATUFC is not a separate program it is simply a run of SATALL with effectively zero assignment simulation loops and only the SAVEIT step included As a consequence it therefore requires that the original trip matrix ufm file is available However post 10 8 if the original network were based on an elastic assignment the SAVEIT assignment uses a fixed trip matrix assignment algorithm in which case it uses the output trip matrix i e ROADIJ from the original run rather than the original input trip matrix file FILTIJ These algorithms are generally faster and do not suffer from problems of terminating early SATUFC has several advantages If the original ufc file did not converge sufficiently well a better level of convergence may be achieved by increasing NITA_S It may also be computationally efficient to set SAVEIT F in the original network and to only run SATUFC when a ufc file is actually required If NITA is very small and NITA_S large the SAVEIT step may take virtually as long as the original assignment simulation loops UFS files can be sent without their ufc files as the latter can be easily re created By adding an argument UFO to the command line a UFO file may be created at the same time as the UFC file see 15 23 6 below Post 10 8 it also updates th
134. d or QUIET is toggled ON the option remains active for subsequent SATURN commands within SATWIN until they are toggled to OFF The QUICK and or QUIET settings in SATWIN are also applied to DOS command line runs created by the SATWIN ie via the TOOLS SATURN DOS Command Shell menu option The SATWIN settings can be overwritten if QUICK and or QUIET is subsequently explicitly set on the command line 15 55 1 Using SATWIN10 In SATWIN 10 this is done by setting the QUIET and QUICK drop down to ON as shown below E LAUNCH PAD SATURN 10 9 10 LEVEL N3 OBA File Settings Module Run Batch Run Command Line Run Test Networks Tools SATURN Manual Help a f QUICK r QUIET Fi f I Remove All Remove Itemisi Run Items Save Itemis Recent Changes Problems Resolved OFF OFF z Orr gt AT U R N Working Folder CASATWINSTEST Im imm fA Program Folder CASATWIHSSEsES 10 9 10 QUICK QUIET drop down boxes Commands Working Folder oc Click Here To Select Then Press Fe Kep or Click Te 00 00 00 00 00 00 CASATWINATEST 5120257 Apr 15 15 157 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 55 2 15 56 15 56 1 5120257 Apr 15 Section 15 Using SATWIN11 In SATWIN 11 this is done by pressing the QUIET and or QUICK buttons located on the bottom right hand corner of the SATWIN11 interface as shown below Quick ATKINS Quiet mode
135. d to define COBA link numbers see 15 42 3 FILKNB Character Blank The input file used to define COBA link numbers see 15 42 3 FILNOD The input file used to define node numbers see 15 42 6 Notes 1 NAMES will default to F i e sequential numbers if the standard SATURN node names exceed 4 digits since 4 digits is the maximum permitted within COBA format 2 MUC T will only work if a only one network is being processed and b if the number of user classes is less than or equal to 3 in that network If not it is automatically replaced by F Note that the limit of 3 is due to a limit imposed by COBA in its KEY056 record formats 5120257 Apr 15 15 105 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 42 3 15 42 4 5120257 Apr 15 Section 15 3 Similarly MVC T will only work if a only one network is being processed and b if the number of vehicle classes is less than or equal to 3 Vehicle class flows are obtained by summing over their constituent user class flows Clearly both MUC and MVC cannot be T at the same time 4 Post 10 9 user and or vehicle class flows may be output as either PCU hr or vph depending on whether parameter PCUS T or F Defining COBA Link Numbers using KNOBS data The default link numbering system used by SATURN to define link numbers in the created coba formatted network is as mentioned above 15 42 1 to use the essentially arbitrary numbering
136. data sources in using OS based co ordinates and it may therefore be a good idea to bite the bullet and transform your arbitrary co ordinates into OS NOW For further advice on how to do so please contact DVV Calibrating bmp files By calibration we refer to the process by which the four corners of a particular omp file are established in terms of the co ordinates used by the network Ideally 15 110 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 43 4 5120257 Apr 15 Section 15 as we have pointed out above both should be based on the same system and the coordinates of the four corners should be established a priori However in the absence of such information a procedure has been established within P1X to obtain this information In order to carry out this procedure the user must be able to identify the network based co ordinates of two points within the bitmap display Ideally these two points should be as far away from one another as possible and near one or the other diagonals Normally the points will correspond to nodes for which the network co ordinates are known although in principle they could be any points which can be easily identified in network terms Formally the bitmap is displayed with a thin red strip added along the edges and a further red cross displayed in the centre The user is asked first to move and click the mouse over the red cross in order to confirm the ce
137. defining V as the flow for that user class Equally we could define marginal cost for a particular class of flows such as buses Note that user class is defined here in terms of the class of vehicles affected as opposed to the class of vehicles which is causing the changes In particular if we increase the flow on link a by 1 pcu it does not matter which class of vehicles is being increased since say 1 pcu of user class 1 has the same effect within the simulation as 1 pcu of user class 2 Note that in this context it is very important to distinguish between marginal cost and marginal time since the conversion between the two will depend on the value of time defined for that user class If as is most likely the case users require the total marginal cost in terms of say pence as opposed to total marginal time then it is necessary to calculate marginal time for each individual user class weight that by the appropriate value of time for that class and then sum over all user classes It is not really possible to define an average value of time since the distribution of flows by user class will vary by turn By a similar token please note that MECC is always calculated per pcu and that different user classes may also have different values of pcu vehicle Again it is up to the user to take account of these factors in terms of translating SATMECC outputs into actual toll per vehicle Alternative Modifications to Incremental Simulation
138. difference V2 V1 and the relative difference V2 V1 VBAR where the average flow VBAR 0 5 V1 V2 The reason for introducing such a statistic is the inability of either the absolute difference or the relative difference to cope over a wide range of flows For example an absolute difference of 100 pcu h may be considered a big difference if the flows are of the order of 100 pcu h but would be totally unimportant for flows of the order of several thousand pcu h Equally a 10 error in 100 pcu h would not be important whereas a 10 error in say 3000 pcu h might mean the difference between building an extra lane or not 15 13 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 7 5120257 Apr 15 Section 15 Generally speaking the GEH parameter is less sensitive to such problems since a modeller would probably feel that an error of 20 in 100 would be roughly as bad as an error of 90 in 2 000 and both would have a GEH statistic of roughly 2 The following table gives an indication of various levels of GEH values both qualitatively and quantitatively Value Comment Examples GEH 1 0 Excellent 65 in 4 000 25 in 500 GEH 2 0 Good 130 in 4 000 45 in 500 GEH 5 0 Acceptable 325 in 4 000 120 in 500 GEH 10 0 Rubbish 650 in 4 000 250 in 500 Thus as a rule of thumb in comparing assigned volumes with observed volumes a GEH parameter of 5 or less wo
139. duced the demand model usually requires a few more loops to achieve the same GAP SD value of lt 0 2 say typically an extra three or four loops reflecting the slower descent in this example Nevertheless there was an overall saving of around 50 in the total CPU time required compared to the standard method as shown below in Figure 15 13 Figure 15 13 Comparison of Highway Model Runtimes by Demand Loop 25 00 Standard 20 00 oO CASSINI Time Saving 4 5 6 15 54 4 Compatibility with SATURN Multi Core CASSINI is fully compatible with SATURN Multi Core the new multi threaded version of the SATURN assignment program The recent testing work using the 10 00 Cumulative SATURN CPU hrs Qi 100 oe i 1 2 3 4 5 6 7 8 9 10 1 2 3 Demand Model Loops 5120257 Apr 15 15 151 Section 15 SATURN MANUAL V11 3 SATURN Special Options and Facilities 15 54 5 15 54 6 15 54 6 1 5120257 Apr 15 Section 15 GBMF modelling system demonstrated that using Multi Core has reduced overall CPU times by a further 25 as shown below in Figure 15 14 below Figure 15 14 Performance of CASSINI and SATURN Multi Core 40 00 35 00 B SATURN E Demand Total CPU for all Operations hrs Standard Method Parallel Plus CASSINI Plus CASSINI amp Multi Core Assignment Convergence Strategies To operate CASSIN
140. duction P1X SATDB and SATLOOK contain various options with a large degree of overlap which allow trees or minimum cost paths to be built from an origin to a selected destination zone or indeed to all destinations The cost used to build a minimum cost path is defined as a linear combination of time and distance or distance related parameters as follows c attad t gt bd where c is the cost on a link t is the link travel time including any 44444 time penalties d is the link distance m is a monetary toll if any a and as are the values of time and distance respectively generally set by parameters PPM and PPK and possibly disaggregated by user class dk k 1 K are the additional link KNOB properties bk k 1 K are conversion factors to reduce them to a common cost see 7 12 2 For most applications the KNOBS facility will not be invoked and cost is therefore a linear combination of time distance and possibly tolls Weighting parameters 5120257 Apr 15 15 59 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 24 2 15 24 3 5120257 Apr 15 Section 15 PPM and PPK will already have been defined by the user during the SATURN runs and if the user wishes to re create the same or similar trees the same values should be selected These values may also have been user class specific However alternative cost trees may also be investigated e g you may run
141. e as defined by FILGAP and determine the number of loops undertaken so far by the demand model and resulting demand model convergence Read the CASSINI Control file as defined by FILCAS Match the number of demand loops undertaken and the strategy to apply as defined by the Loop Threshold So for example if there are two strategies an initial strategy for the first loop and a second defined for loop 5 onwards i e LoopThreshold 5 and four loops have been undertaken so far the first strategy will be applied Within that strategy compare the current demand model GAP SD value against the various GAP SD ranges GAPVALUE and export the parameters to the XCP file An example of the control file is provided below EXAMPLE OF THE CONTROL FILE C UltraEdit 32 C ASWO9 DIADEM_CASSINI_SLO15 CassiniControl txt Cow o a mh ne amp Ph Pe FREE mo H l3 l4 15 l6 1l 1 193 20 Zl zz 23 24 25 26 zY zZ 23 30 31 J oO CassiniContral tck T Lo Advanced Window Help Hse vege 20 peta Rev bs poe oa SURES PGE Bauer EU OTTEESEEN EEEE EE ELS EEE RO PLONE OREO DIGDEN Grotley Version 3 0 11 06 09 amp PaARan amp END LOOPTHERESHOLDE 1 GAPYALUE 3995 STPGAP 20 00 UNCRTS 10 00 NISTOP 1 NITA 5525 SAVEITH T MaASL 20 GAPYALUE 100 aTPGAP 15 00 UNCRTS 5 00 NISTOP 1 NITA 3525 SAVEIT T MASL 20 GAPYALUE 20 STPGAP 10 00 UNCRTS 5 00 NISTOP 1 WITA 5525 SAVE
142. e not all links need to be included missing links default to zero Note that if a link A B is included in the 33333 buffer records but has already been coded as part of the simulation network it will be ignored as a buffer link but the KNOBS pieces of extra data will be associated with the simulation link In this respect the capacity index input in columns 43 45 is equivalent to extra data since it too is associated with simulation links Storing Knobs Dirck Access Codes Once processed by SATNET via whichever format each Knob is stored on the output ufn file with Dirck Access Codes Section 15 21 2303 for the first data field 2313 for the second etc The data thus created may then be displayed using either P1X or SATDB by referring to those DA codes Transferring Internal Knobs Data to an External File As noted earlier 15 14 5 we strongly recommend that KNOBS data be input via an external ascii file KNBFIL rather than internally under the 33333 data In order to assist users who have data stored internally to transfer the data to an external file two useful facilities are provided post 10 8 16 Firstly a procedure knobdump bat based on SATDB has been created in order to dump existing KNOBS data within a UFS file independent of how that data was Originally input into an output ascii file with the correct format for re input as a KNBFIL Secondly an option has been included within P1X Network Editing to del
143. e ufs file to correctly set SAVEIT and or SAVUFO to T so that subsequent analysis programs such as P1X will know that the UFC UFO files should exist Post 11 1 if the original network were run using OBA then SATUFC will in effect generate a set of O D paths in a UFC file which approximate the same final set of link flows Thus the newly created UFC file and the original UFO file fulfil similar functions in terms of post assignment analysis e g select link analysis but the UFC file has the advantage that it may be used in certain programs such as SATPIG where the UFO file may not Similarly a UFC file may be generated from a path based assignment where the UFQ files which store the paths may also not be suitable for all forms of post assignment analysis 15 55 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 23 6 132360 1 5120257 Apr 15 Section 15 Note that if using SATUFC with either a path based or OBA original solution it may make sense to copy and rename the original ufs file so the two sets of solutions may be used independently Alternative Formats for Saving O D Routes UFO and UFQ files The ufc files described above are relevant to assignments done using the Frank Wolfe link based algorithms MET 0 Path based and origin based assignments use their own particular techniques to preserve route flow information and in addition link based routes may also be conver
144. e achieved by appropriately reducing the convergence targets for the SATURN highway model where possible Figure 15 11 Typical SATURN Model Convergence Profile CPU Time 0 10 20 30 40 50 60 70 80 90 100 9 00 8 00 7 00 6 00 5 00 4 00 3 00 2 00 1 00 0 75 0 50 0 25 0 10 0 05 GAP Assignment However SATURN may also be embedded within a larger demand model structure aka VDM Shell in which the trip matrices are not fixed but are variable and cost dependent and this larger model structure must also converge to an equilibrium solution see 7 4 1 Typically some form of cobweb loop between supply assignment and demand see 7 4 5 is used in order to achieve equilibrium between the two sub models as illustrated in Figure 7 8 We may quantify the degree of convergence between successive loops of the demand models by a supply demand gap value as given in TAG Unit M 2 and defined by Fion C Xion P C Xion Xion GAP SD 100 where Xictm is the current flow vector or matrix from the model C Xicim is the generalised cost vector or matrix obtained by assigning that matrix 15 149 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 D C Xictm is the flow vector or matrix output by the demand model using the costs C Xictm as input and ijctm represents origin
145. e as 1 but uses a different algorithm to achieve it Experience to date is limited certainly in certain situations it performs much better but whether there are other situations where it performs worse is not yet certain Nonetheless it is recommended over 1 Each algorithm follows an iterative strategy whereby green time is swapped between the best and worst stages with the amount of green time swapped being the local optimum After each swap the best worst criteria are recalculated 15 80 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 31 4 5120257 Apr 15 Section 15 and the next pair identified While fairly reliable such an approach is not guaranteed to produce a global optimum under certain circumstances the algorithm may stick and the apparently best pair for swapping may not in fact lead to any improvement For this reason the maximum number of iterations is user set in order to prevent infinite loops Further outer iterations may also be required since once new stage times have been generated a re simulation of that node may change some of the criteria on which the optimisation was based e g lane sharing may change A further user set option specifies the maximum number of outer iterations allowed default 1 since in most cases a re simulation and re optimisation has no effect Finally it should be noted that the optimisation procedures all assume that stage times
146. e name of the ASCII CSV file reporting the convergence of the demand model Default blank i e no file defined at this stage Note that the convergence parameters in the SATURN network file should be relaxed as these will be applied for the assignment of the first demand model loop These will be subsequently overwritten by XCP produced by CASSINI CASSINI CONTROL FILE The convergence strategy is defined in the CASSINI Control file as specified by FILCAS parameter The strategy is defined by setting a series of GAP SD thresholds which for a given GAP SD or lower in the demand model the user defines the parameters that CASSINI will export to the XCP file The parameters are a sub set of those normally contained in the PARAM amp END section of the 5120257 Apr 15 Section 15 15 153 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 network data file in particular those that relate to convergence options within SATALL as shown in the table below N B the list may be extended if necessary The current list of parameters that may be changed by CASSINI is as follows with the new v11 2 parameters in italics amp OPTIONS UPDATE WSTART DIADEM amp PARAMS SAVEIT UFC109 FISTOP STPGAP XFSTOP UNCRTS MASL KONSTP ISTOP MET NISTOP NITA_M NITA_C NITA_S NITS NITA SPIDER MULTIC ILOVEU NITS_M SAVUFO AK_MIN The user may also provide more than one
147. e net buf Added in version 10 9 15 SATCCS Converting Simulation Centroid Connectors to Buffer An extra batch file introduced in Release 11 1 code named SATCCS performs essentially the same job as SATBUF but operates on simulation centroid connectors instead of simulation links Thus the command SATCCS net creates an output text file net map with link data in the 33333 format for simulation centroid connectors only Thus tf a zone Z is connected to simulation link A B then there will be a record A Z and another from Z B with appropriate distances times etc etc The intention would normally be that the file map dat would be included within the 33333 section of a buffer only network dat file either verbatim within the 33333 data segment or perhaps preferably as a INCLUDE file See 15 1 5 for such an application The procedure uses the dump map links option within P1X see 11 4 2 3 but in a purely off line batch mode and with only simulation centroid connectors selected No special KEY file is required unlike SATBUF Converting Conventional Speed Flow Curves into SATURN Curves General Principles It is very often handy for users with existing networks coded in conventional detail to convert their networks into a SATURN network by stages Thus the first step would be to code the existing network as a buffer only network presumably using a computer program to carry out the necessary changes in format with no simula
148. e same way that total pcu hrs and total pcu kms are reported For further details as to how tolls are handled within SATURN please see Section 20 3 Creating Knobs Data In order to use this facility the user must first define the number of data items to be input the amp PARAM namelist parameter KNOBS Secondly the link data itself must be input to SATNET and that in turn may be in one of three forms 1 as an additional second record for each buffer link with the required number of data fields up to a maximum of 8 see Section 6 6 2 as added data items at the end of the first and only buffer link data records 3 asa separate free standing input file FILKNB Option 3 an external ascii file is highly recommended for ease of use and for avoiding possible errors The parameter KONAL Knobs ON A Line distinguishes between i and ii KONAL F and T respectively Option iii is only used if a file is nominated by the character variable FILKNB or KNBFIL If FILKNB is set it is assumed that no Knobs data appears in the network dat file itself and KONAL is irrelevant Note that under i the extra record may be entirely blank in which case it is read as a string of zeros See 15 29 Equally blank inputs under ii are also interpreted as zeros 15 34 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 14 5 1 External KNOBS data files FILKNB The designated file FILKNB normally has a standar
149. e via PLDFIL whereas the first would have PLOD F the default In effect the PLOD option allows the heavy lorries to have the first choice of route and implies that whereas lorries can affect the routes subsequently chosen by the normal vehicles the normal vehicles cannot in turn affect lorries In some circumstances this may not be a totally unrealistic assumption however allowing 15 10 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 5 2 15 5 3 15 5 4 5120257 Apr 15 Section 15 for interaction in both directions would no doubt be preferable and is provided by Multiple User Class Assignment Section 7 3 While the lorry network can have different network properties from the normal network e g different link speeds etc both networks MUST be structurally identical i e have the same nodes links and turns unless a text file is used see 15 5 4 N B PLOD differs from PASSQ and or UPDATE in this respect the PASSQ UPDATE networks may have a different structure from the main network see notes 1 in section 17 3 1 and section 15 3 respectively Hence strictly speaking it is not yet possible to introduce lorry bans by banning turns or removing links in the lorry network However lorry bans can in fact be introduced by certain relatively simple tricks For example you can effectively ban lorries from a link by giving that link an extremely high travel time in the lorry network
150. eating a link as though it were part of the road network while clever old you give it characteristics more appropriate to a pedestrian than a car How such coding tricks are accomplished is of course up to the user One common method assuming that the walk networks are superimposed on a simulation network is to code the walk links and nodes as part of the buffer network with low fixed speeds times a flat flow delay curve power 0 and effectively infinite capacity e g 99999 The walk links are then connected to the simulation network via external simulation nodes The origin destination zones to from which trips exit enter are then connected to walk nodes rather than simulation links Thus an o d trip with a destination which requires walking will be assigned a route which starts at a normal zone and initially follows a set of normal i e car links until it reaches the walk links through which it can reach its destination At this point in effect the car becomes a pedestrian although as far as SATURN is concerned nothing has really changed it is simply finding a route through a network The same principle works in reverse for trips which start as walk trips lf very naturally the point of transition from car to walk is at a car park note that tolls and capacities may be associated with the car park as described in Section 20 5 3 Certain presentational problems may occur in P1X if for obvious reasons
151. ed by characters beginning with a They may be further sub divided into two groups link types and format i Those that select the link types to be output Under link selection the following characters indicate link types to be included SL Include simulation links i e roads ST Include simulation turns SCC Include simulation centroid connectors BL Include buffer links BCC Include buffer centroid connectors and the composites L Include all simulation and buffer links CC Include all simulation and buffer centroid connectors Including an X immediately after indicates exclude that link type e g XST implies exclude simulation turns but leave the other 4 types For example DBDUMP net net txt 4503 SSL would dump demand flows for simulation links only to file net txt ii Those that control the format Further options controlling the output formats e g nodes in fixed columns versus free format CSV are being added to match some of the interactive options within SATDB Thus KP5COL Nodes are output in fixed columns of 5 or KP6COL in fixed columns of 6 Note that if the node or zone numbers in the network being dumped exceed 4 digits then the output link format automatically allocates 6 columns per node The 5 column option may be set by default by defining the parameter KP5COL T in the preferences file p1x0 dat KPS5COL F selects 6 columns Furthermore if the filename of the output fi
152. ed in the buffer network with their buffer only connections i e those links to or from other nodes in the buffer network Thus links such as E B above would be included under 33333 3 In constructing the joint buffer simulation network SATNET ignores an input buffer link if either of the nodes has already been defined in the simulation network unless both are external simulation nodes This means that a user progressively re defining a section of a large network as a simulation network does not need to remove simulation links from the buffer network input However some care needs to be exercised here that all inner nodes have indeed be defined as simulation nodes since otherwise spurious buffer links may creep into the middle of the simulation network 4 On the other hand the data on an ignored buffer link e g the time and distance is not totally ignored in that it is compared to the comparable simulation data in order to check for self consistency In addition the buffer link data may be used to supplement the simulation data as explained further in Sections 6 6 15 13 and 15 14 5 We also note that problems may occur due to U turns from the simulation network at the simulation ouffer boundary as described in detail in Section 18 9 Automatic Network Coding The AUTOX and AUTOZ Options The AUTOX and AUTOZ options are essentially labour saving devices which remove the necessity for the user to code external simulat
153. ed within SATNET by basing it only on errors 15 178 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 59 15 59 1 5120257 Apr 15 Section 15 which have been included within the ERL file but with extra tests based on values stored in the first and or second extra data fields In both cases a critical value needs to be defined by the user but its application differs between whether data from Field 1 or 2 is to be used Thus with Field 1 the test is based on equality i e if you set a critical value of 1 only those error records which have a 1 in Field 1 will be selected Under 2 the test is greater than or equal i e all entries whose Field 2 value gt the critical value are selected In addition the second field differs in that the colour used to highlight the selected nodes depend upon the value in the second field Thus a low value might be displayed with a light colour and progressively higher values with progressively darker colours in order to indicate possible degree of urgency as set by the user The pens to be used for different numerical values are pre defined within the program but may be over written using parameters NP_ERL n within the most recent preferences file P1X0 DAT We repeat the information given above that at the moment Field 1 is set as either O or 1 within SATNET depending on whether an error is old or new whereas Field 2 is intended to be manipulated
154. edure the nodes which lie on the boundary between the simulation and buffer networks at any stage MUST be included as external nodes in the simulation network unless one uses the AUTOX facility as described in Section 15 12 COBA 10 Speed Flow Curves The form of the DfTl recommended speed flow curves was replaced in the late 1980 s by the so called COBA 10 curves with two sloping linear segments as opposed to Advice Note 1A above which had a flat segment followed by a linear Slope Figure 15 1 below illustrates the new form for flow V less than capacity C They are still in use to the present day 2007 although the specific numerical values for individual curves are out of date N B The x axis or flow axis in Fig 15 1 is specified in units of vehs hour whereas SATURN see 15 17 1 generally works in terms of PCUs hr some conversion may therefore be required if one wishes to fully translate COBA curves for use in SATURN See 15 9 4 below 15 21 SATURN MANUAL V11 3 i SATURN Special Options and Facilities Figure 15 1 COBA 10 speed vrs flow curves kph 110 100 90 80 70 60 50 40 2000 4000 6000 8000 Vehs hour direction The following equation describes the relationship S S S V F V lt F S V 458 S S V F C F F lt V lt C S 1 S V C 8dC V gt C Where So is the free flow speed S4 is the intermediate break point speed S is the speed at capacity C A best fit value of t
155. efined interactively and the disaggregate data re calculated In addition the link selection rules as set within SATDB may also be applied on top of the normal link disaggregation rules but only if SATLOOK is being accessed via P1X A further P1X only option allows the indices which define sub sets of links to be set via an existing integer data base column Alternatively the link indices may be input directly from a L2G text file which gives the required index for each link see 15 60 4 for formatting rules 15 180 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 60 15 60 1 15 60 2 5120257 Apr 15 Section 15 Node and or Zone Aggregation Files General Principles and File Extensions A set of filename conventions has been drawn up in order to identify ASCII text files which define the mapping of one set of node zone definitions into another Thus a file with extension Z2G will contain data which specifies which Groups are to be associated with each Zone Z2S maps Zones into Sectors N2G maps nodes into groups G2S maps groups into sectors etc etc The following letters may be used N for nodes Z for zones D for districts B for boroughs and S for sectors In addition T represents text so that a G2T file would consist of a series of group names followed by a text description of that group e g 1 Otley As a matter of good practice and common sense it is prop
156. efore the batch file proceeds to the next command This introduces a short pause before the next instance of the SATURN program that is to run in parallel is called In other words if the user wishes to run two instance of SATALL the user should request a small pause between the first and second runs commencing to prevent potential file access errors arising Note that WAIT has to be used within a batch file it will not wait as a single command line call An Example An example of a batch file to undertake a parallel run of the SATURN module is annotated below but the process would also readily work with other SATURN modules including SATALL SATPIJA SATLOOK SATME2 and SATEASY for example The batch file should contain the following commands PATH 3 C2 Annn EE 1 sets the path to the folder containing SATURN programs if required SET INPUT1 EPSOM5000 2 sets the input parameter for the first SATURN run as an environment variable In this example the network and matrix file have the same root name i e EPSOM5000 UFN and EPSOM5000 UFM hence only one environment variable i e INPUT1 is required If the root names were different two environment variables would have been required one for the UFN file and one for the UFM file Sid LIN UNL che COMS 00T 3 sets the input parameter for the second SATURN run as an environment variable The root name of the network and matrix file is the same in this example
157. elected flows is MUCH easier to appreciate in a graphical format On the other hand SATDB may be easier to use in conjunction with key files SATU2 has effectively been superseded by P1X and or SATDB and is less convenient its use is not recommended So the best buy recommendation is to use P1X in the first instance Finally we should note the caveat expressed in Section 15 23 2 that under certain circumstances e g elastic assignment select link analysis as with other similar analyses is based on an approximation and that the select link flows need not be entirely consistent with the true flows In these circumstances the select link results should be viewed as indicative rather than exact The difference statistics 15 44 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 20 5120257 Apr 15 Section 15 generated within SATALL based on the errors from all links may be used as a rough guide to the errors to be expected on any single link analysed The Dutch Option Long Node Numbers The DUTCH option has been introduced to allow nodes with up to 8 digit node numbers to be defined in buffer networks so called because it is common practice in The Netherlands The major effect of this option is to change a number of the input formats so that node numbers in certain circumstances occupy 10 columns of data input as opposed to 5 Note that simulation nodes are still restricted to 5 digits al
158. ely easy convergence criteria for the initial SATURN runs when the trip matrix to be assigned is still in flux but to tighten up those criteria once the demand trip matrices begin to stabilise While this may potentially increase the overall number of cobweb loops required to achieve convergence the expectation is that that increase will be more than offset by the CPU saved on earlier loops where internal SATURN convergence is much faster We may note that this process of relaxed convergence is very similar to that used by AUTONA see 9 5 4 whereby we set easy assignment stopping conditions when the assignment simulation loops are poorly converged in order to minimise assignment CPU but tighten them up as the assignment simulation convergence improves By setting a more relaxed highway convergence target for the early cobweb loops using CASSINI considerable savings in CPU time may be achieved as the over convergence of the highway assignment is reduced These two convergence profiles are also shown below in Figure 15 12 15 150 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities Figure 15 12 Typical Demand Model Convergence Profile Demand Model GAP 60 SATURN CASSINI Convergence GAP Variable GAP Supply Demand 30 Standard SATURN Convergence GAP 0 05 N Q o 10 0 Demand Model Loop 15 54 3 Performance Gains With CASSINI intro
159. en flows for example to outliers For example errors of 63 and 126 in 1000 pcu hr give GEH values of approximately 2 and 4 but chi squared values of 4 and 16 GEH effectively says that an error of 126 is twice as bad as 63 not four times as bad These differences are reflected in aggregate measures such as the average of all GEH Statistics from a set of counts With version 10 1 the GEH statistic comparing two database columns in SATDB P1X may be calculated as an explicit function see 11 10 8 Use of SATURN Outside the U K Although SATURN has clearly been set up in the U K and with U K applications in mind it has been programmed in a perfectly general manner so that with minimal changes it could be applied in other countries e g in Australia and New 15 14 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 7 1 15 7 2 5120257 Apr 15 Section 15 Zealand using the NOTUK parameter and in countries where vehicles drive on the right using LEFTDR The NOTUK Parameter Setting NOTUK NE 0 in the PARAM namelist input causes the model to make a number of assumptions concerning priorities for turns coded with one of the priority markers described in Section 6 4 2 which differ slightly from the assumptions made in the U K They are as follows Opposite right turning vehicles for example at traffic signals do not interfere with one another whereas in the U K it is assumed that they execute a
160. enables certain SATURN applications principally MX and SATALL to run quietly in the background without creating S any pop up windows during their operation Network Aggregation SPIDER Basic Principles Network aggregation is a technique whereby links and or nodes in the basic assignment network may be combined together into an equivalent set of aggregated links nodes with the objective of reducing the cpu time required to carry out the basic assignment steps of tree building and loading For example as illustrated below a one way link from A to B followed in series by a one way link from B to C so that node B has only one entry and one exit may be replaced by a one way link from A to C with a cost equal to the sum of the costs on A B and B C Thus we have reduced two links to one link and removed node B while at the same time retaining the same cost of travel between A and C so that if links A B B C are part of a minimum cost path from a particular origin in the original network then so is A C in the aggregated version of the network A gt B gt C A gt C The cpu time required to build a minimum cost shortest path tree from a single origin to all nodes in a network may be estimated by formulae such as for the d Esopo algorithm most commonly used in SATURN Tepi a a2 N nodes ag Niinks 1 a4 Saqrt N nodes See Improved shortest path algorithms for transport networks by
161. entroid connectors to external buffer zones see 15 56 2 4 Remove any bus only links since they will never form part of minimum cost paths for trips in the trip matrix 5 Aggregate all nodes which have a single exit with one or more entries N B this will include all dummy 2 arm nodes 6 Ditto but with nodes with a single entry and or more exits 7 Aggregate all nodes with progressively 3 arms 4 arms etc etc up to a maximum of MAXSPA arms Thus at the end of each step a new aggregated network is created and passed to the following step for further aggregation Steps 5 to 7 are repeated iteratively with the maximum number of arms increased by one on each pass Thus on the first pass all 3 arm nodes are aggregated in step 7 on pass 2 all 3 and 4 arm nodes are aggregated etc etc The iterative loops are repeated until no further aggregation is feasible or the maximum number of arms per node which may be aggregated reaches MAXSPA as set in amp PARAM with a default value of 15 A further rule is applied in step 7 which is that a node is only aggregated if in addition to having less than a certain number of arms it also satisfies the highly empirical rule that Nnew lt 23 Nn Not Now 2 Where Nin the number of in bound directional links Nout Out bound links Now Number of two way arms Nnew Number of new direct links that will be created Nin Nou Now For example aggregating a 6 arm node w
162. equire roughly the same CPU time with or without FCF although we would expect a reduction in overall CPU time with FCF due to a reduced number of assignment simulation loops Modelling FCF nodes within a Simulation Network Those nodes which are designated as fixed cost flow within a simulation network are identified and this is purely a technical detail by an extra binary bit within an 15 2 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 1 4 5120257 Apr 15 Section 15 array containing node properties DA code 254 to be more precise The following two sub sections describe how this may be accomplished here we describe the modelling differences and similarities between a normal simulation and an FCF simulation Both styles of node simulation start with IN profiles on all input arms see Section 8 1 and create OUT profiles along with delays The difference is that the FCF method is based purely and simply on the parameters in equation 8 5 above and section 8 4 2 rather than by a full simulation of interacting flows over short time unit Thus under FCF the maximum OUT flow is determined by the minimum of a the IN flow and b the fixed turn capacity C in equation 8 5 above The delay is set by use of equation 8 5 for the current flows V Note that the modelling of IN OUT flows ensures that the assigned flows are correctly modelled within the FCF network and that any flow metering
163. er diagonal link will be created from C to B with cost CA plus AB For all origins with costs fixed only one of the two alternative CB links may possibly appear in the minimum cost tree that version which has the lower cost Note that it is quite possible that neither link appears in the minimum cost tree if B has an entirely different back node Thus if we eliminate the more expensive link between C and B prior to tree building we will save time on tree building since only one version of link CB will ever be considered as a candidate for inclusion in the minimum cost tree Unfortunately it is not possible to totally eliminate one of the duplicates once and for all since the one to be eliminated depends on the current definitions of link costs which change throughout the assignment process However for a particular iteration of Frank Wolfe where the costs are fixed it is possible to eliminate the more expensive alternative and therefore save cpu time for each origin zone s tree build This modification has therefore been introduced into the Frank Wolfe algorithm applied to aggregated networks and is found to reduce total cpu significantly Duplicate links do not need to appear just as pairs it is quite feasible for several duplicate links to exist between the same two nodes so that eliminating all but one reduces cpu time still further 15 56 5 2 Separate Centroid Connectors from Real Links 5120257 Apr 15 Section 15 Tree buildin
164. er than changing the value of USESPI in the preferences file the choice may be made by including the token USESPI on the command line Hence SKIMDIST net matrix USESPI Requests a distance skim on net ufs with skimmed output to matrix ufm but with the parameter USESPI definitely set to TRUE independent of its default value and or any value set in the preferences file SATLOOKO DAT Similarly the command SKIMDIST net matrix USEUFO 15 73 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities Requests the use of a UFO file for skimming rather than a UFC file again assuming of course that both UFO and UFC files are available In this case the default choice is set by USEUFO as defined within the network dat file Other command line tokens include USEUFC use UFC in preference to UFO NOT USEUFO do not use UFO and hence equivalent to USEUFC NOT USESPI do not use a Spider Web network and NOT USEUFC use UFO instead of UFC These options were first introduced in release 11 1 11 in July 2012 15 27 8 Post 10 9 17 Skimming Algorithms NUSKIM T Releases 10 9 17 and beyond include a new set of algorithms to carry out OD skimming within SATLOOK which should be more cpu efficient than the older versions Essentially they employ a once through algorithm rather than tracing each O D path separately The new algorithms may be invoked by setting a namelist parameter
165. erent values of NUC should be used if it is desired to have greater or less resolution of cyclical flow profiles at a particular junction For example if the entry profiles to a roundabout are virtually flat there is no particular reason to divide the cycle period into a large number of small time units which will be virtually identical to each other Here a small value of NUC gives the same results at less computing cost On the other hand traffic signals with a large number of relatively short stages benefit from the extra resolution of short time units i e a large value of NUC Traditionally and as a very general rule in SATURN our advice has always been to stick to the global values unless there is a very good reason for changing NUC locally However post 2007 the benefits of increasing NUC under certain fairly specific local circumstances have become better recognised and extra parameters have been introduced in 10 8 to help deal with these issues In particular using larger values of NUC at complex signalised junctions may have benefits for improved convergence Thus for example with X turners at traffic signals which are partially blocked by opposing traffic during a green phase it is important for the simulation to be able to accurately estimate the point during the phase at which gaps begin to appear in the opposing traffic and the X turns can begin to clear albeit possibly very slowly This is particularly so if the green phase
166. ers headed by amp PARAM and terminated by amp END The default file satcoba0 dat sets all defaults The following parameters may be set 15 104 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities Table 15 1 SATCOBA Namelist Parameters OPTION TYPE DEFAULT INTERPRETATION NAMES Logical T lf T use standard node names in the output file if F use map based sequential numbers 15 42 6 DEMAND lf T use demand flows if Fuse actual flows SUMNET Logical F If T add the link flows from each input network and output their sum if F output individual flows MIDLF Logical F If T define simulation link flows mid link not downstream MILES Logical F If T output link distances in miles else kilometres MAJORM Logical F If T the turning matrix for all priority junctions is output in the order of a major arm first followed by a minor arm MUC Logical F If T flows are output separately for up to 3 user classes all from network 1 in the KEY056 records MVC Logical F If T flows are output for up to 3 vehicle classes from network 1 in the KEY056 records PCUS Logical iT If T user vehicle class flows are output in units of pcu hr if F they are converted into veh hr N B This does not apply to total flows only disaggregate flows COBAF 1 Factor to be aii to the flows on input Comm ret 1 Eee soci twsone COBAF2 Real 1 0 ditto network 2 up to COBAF4 ditto network 2 up to COBAF4 KNOB Integer The SATNET KNOB field use
167. es 8 nodes out of13 and 8 links out of 14 Z A2 B2 Note that if the spigot node S has been coded as a buffer node under 33333 see Section 16 6 3 then a third mini node is created at S has shown below This however does not change the general principle that zone Z is connected via aggregate centroid connectors to nodes A and B but it does increase by 2 the number of assignment links replaced 15 162 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities S S2 S We may further note see also 16 6 4 that the above buffer node connector allows possible U turns via S S3 S in the full network but that this possibility is explicitly excluded in the aggregate network since e g there is no aggregate link created from A to A2 which would correspond to a U turn 15 56 2 4 Spigot Centroid Connectors in General A more general variation on the spigot centroid connector configuration occurs when the simulation node M is connected to more than 2 other internal simulation nodes In this situation a mini aggregation may be invoked by substituting direct centroid connector links from M1 to Z and from Z to M2 in Figure 15 x with a reduced number of zones and or links removed However see step 2 in 15 56 3 it is still an aggregation step worth doing 15 56 2 5 Some Properties of Aggregate Networks 15 56 3 5120257 Apr 15 Section 15 The final aggregate network will consist of a sub set of the original nodes
168. esolution and every stage transition occurs at an integer time unit see point 3 below under AUTNUC In versions of SATURN prior to 10 8 there was an upper limit of 25 on the value of NUC both globally and at individual junctions in 10 8 this has been increased to 125 for individual junctions or for junction types i e NUCJT but the maximum of 25 is still retained as the global default value Other relevant changes in 10 8 include 1 Warning 94 and or Serious Warning 153 have been introduced to detect values of NUC per node which are judged to be too small seriously too small 2 A subscripted parameter NUCJT j j 1 5 has been added to set a default value of NUC for all simulation junctions of type j NUC continues to function as a global default which may be over ridden by NUCJT for specific node types 3 If AUTNUC T then in processing a network dat file SATNET will automatically choose an optimum value of NUC per node if the default value is judged to be too low up to the above mentioned maximum of 125 Thus in extremis AUTNUC will set NUC equal to the cycle time for that junction so that one time unit equals one second N B Increasing NUC for all nodes may lead to problems with array dimensions being exceeded and indeed this is one reason why in the past users may have been forced to reduce NUC from the former default value of 15 down to say 10 Indeed post 11 1 the default value has been dec
169. ete all existing second line KNOBS data from the 33333 data segment Thus by following both the above processes and adding a reference to KNBFIL within PARAM the KNOBS data is effectively transferred into a new format 15 36 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 15 15 15 1 15 15 2 5120257 Apr 15 Section 15 Note that if the data was originally stored at the end of every buffer record KONAL T method 2 in 15 14 5 it is not strictly necessary to delete it from the 33333 data since if KNBFIL is set the end of line buffer data will never be processed Node Dependent Parameters GAP GAPM NUC and LCY As explained in Section 6 4 1 there are four parameters GAP GAPM NUC and LCY which can be set individually for nodes as opposed to using global default values using data values input on the node record GAP and GAPM GAP and GAPM require little further explanation they should be used when it is felt that due to the specific physical lay out of an intersection gap acceptance is either easier or more difficult than at an average intersection Node graphics editing within P1X may be used to help determine appropriate values See also Section 15 22 We also repeat the warning in Section 15 22 that the default values of both GAP and GAPM are probably highly unrealistic and should be changed if not on a global basis than certainly on a node by node basis NUC Diff
170. etting USESPI The resultant skimmed matrices are the same whether or not the aggregated network is used the main difference is that the aggregated method requires significantly less CPU time The use of aggregated networks applies to both skimming a single tree as well as to forest based average skimming For forest based skims the potential CPU time reductions are significant e g 10 times faster however for a single tree build operation per origin user class not multiple iterations CPU time Is less of an issue here in absolute terms Note however that at the time of writing the possibility to use aggregated skimming applies to most but not all applications of skimming Its use is being gradually extended and will eventually cover all applications Information within the LP files should hopefully make it clear whether it is being applied or not For further information see 15 56 7 1 Command Line Over rides for e g the use of UFO files The command lines associated with procedures such as SKIMDIST SKIMTIME etc etc may also be used to over ride certain default skimming options For example the choice of whether or not to use a Spider Web network representation rather than the normal network assuming of course that the SPIDER network has been created in the first place is normally controlled by a parameter USESPI described above and which may be set in the preferences file e g SATLOOKO DAT However rath
171. fact they occur quite naturally as a result of normal give way conventions For example consider a roundabout with 4 arms north south east and west with a very heavy flow from east to west which effectively blocks all entry traffic from the south In these circumstances the only way traffic from the south can enter is when north south traffic cuts off entry from the east Hence 15 133 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 50 4 15 50 5 15 50 6 5120257 Apr 15 Section 15 an increase in N S flow can reduce the delays from the south leading to a negative contribution to MECC which in turn can potentially drive the total MECC negative as well Disaggregated Marginal Costs by Turn The impact of adding an extra pcu on a particular simulation turn may be disaggregated into increased delays to a pcus making that particular turn b other turning movements from the same arm and c turns out of other arms at the same junction MECC is the sum of all three impacts We refer to these three disaggregate contributions as own MECC arm MECC and interactive MECC Disaggregated Marginal Costs by User Class Vehicle Class etc lf we wish to consider the marginal impact of increased flows on a particular link on e g one particular class of flows as opposed to the total flow on links as implied by the definition of V in equation 15 16 it is simply a question of re
172. fer Sim areas BUT excluding INTRA ZONALS Simulation statistics speed distance time within this time period following time period SATLOOK option 4 Assignment Simulation statistics speed distance time SATLOOK option 5 Average Queue in the Simulation Network SATDB DA Code 1433 15 122 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities Queue at End of Time period in Simulation Network SATDB DA Code 1483 Average Delay Vehicle mins calculated Congestion Index mins km calculated The name of the output file is the network name with a CSV extension eg EPSOM98M CSV 15 49 1 2 SATSTAT Excel Spreadsheet 15 49 2 15 49 2 1 5120257 Apr 15 Section 15 In conjunction with SATSTAT the resulting CSV file s may be imported into the MS Excel spreadsheet called Summary Report v3 02 xls via the Import CSV Visual Basic macro available in the Summary worksheet Once the MS Excel macro is run it will ask for the name of the CSV file to be imported into the spreadsheet and become available in the selection box If selected the network stats will appear in the column below both in summary and more detailed form enabling comparisons to be made between different networks A demonstration is available under Test Networks gt Option 4 Run SATSTAT for Epsom SATSTAT has been successfully tested on all versions of SATURN 10 xx ie 10 1 to 10 8 Please note that it does not disa
173. files SATUFO Single User Class option A sub option within the batch procedure SATUFO BAT allows a UFO file to be created for a single user class n by using a Command SATUFO net NOMAD n in which case the output UFO file will be named net_n ufo 15 23 7 2 SATUFO Multi core option 15 23 8 5120257 Apr 15 Section 15 The SATUFO process will also take advantage of the multi core capability within the software if available see section 15 53 for further details Final Comments The Uniqueness of Route Flows and Other Limitations In applying the various analyses available within SATURN based on specific O D routes users must appreciate that all such outputs must be taken with a rather large pinch of salt 15 57 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 23 9 5120257 Apr 15 Section 15 Firstly it must be appreciated that O D routes are not uniquely specified by Wardrop Equilibrium see 7 1 6 and that the routes generated by the Frank Wolfe algorithm plus OBA are to a certain extent arbitrary Thus strictly speaking Wardrop Equilibrium only identifies those O D routes that may be assigned positive flows but not the precise split of traffic between those routes A simple example is given in Section 7 1 6 to demonstrate the non uniqueness of origin or user class based flows between two parallel routes even when the total link flows are uniquely specified The final assigned route flow
174. flows with the presumption being that they are in pcus hr Equally it applies to all definitions of capacities e g as contained in buffer network speed flow curves One partial exception to the above rule is buses where a the network 66666 definitions of bus routes input frequencies buses hour which are then factored by BUSPCU to give bus flows as pcus hr and b output bus data is sometimes given in terms of buses and sometimes e g when giving total bus flows on links in terms of pcu s Hopefully the text should make it clear what is being printed 15 41 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 17 2 15 18 5120257 Apr 15 Section 15 In the case of Multiple User Classes and stacked O D trip matrices it is further assumed that all the various stacked matrix levels will be in the same units and that their assigned flows may simply be added together Clearly it is vital for users when importing data into SATURN from external sources to check the units of the external data and to adjust as necessary For example this applies to the importing of trip matrices which may be in vehicles hr as opposed to PCU hr speed flow curves etc etc PCU Factors by Vehicle Class SATURN 10 1 introduced an extra parameter VCPCU disaggregated directly by vehicle class and indirectly by user class if necessary see 5 8 which is used to convert pcu s on the recommended assumption that all trip
175. ful for example to make certain links more attractive to traffic The weighting coefficient for KNOBS data defined within the 88888 data set 6 11 is defined in the normal way as a positive number i e it is not possible to create a negative cost by having positive data with a negative weight Note that items of Knobs data which do not contribute to link generalised costs e g for applications as described in 15 14 2 should have their 88888 weights input as zero or blank to avoid being confused with e g tolls Using Knobs to Set Tolls Road Charges A particular example of a knob field used to define generalised cost is when the field directly represents monetary charges tolls As noted in section 6 11 tolls are indicated by including either a or amp symbol in the relevant columns of the 88888 records for that field If the remaining columns are blank then the assumption is that the knob entry is the true charge per link in units of pence but if a numerical factor apart from 1 0 is also included then the knob entry is factored by that amount This allows the user to define tolls in purely nominal units say 1 0 for all links and then let the 88888 records define the specific toll In addition knobs which are explicitly defined as tolls as opposed to the less well specified effects under 15 14 12 are included in the output network statistics from the assignment which report the total revenue generated by tolls in th
176. g X tu urnsiatc signals Nook Mime kere 21 Or 1s 2 00 Turn saturavicom tillows per lane Gditter widely O 11015 0 0 Maximum roundabout turn sat flow exceeds eS el SO SG2 50 l Mule apl e ureo Sineiam iio MUNG Ole alana The records are sorted firstly by B node secondly by A node thirdly by C node and finally by error number If the error is associated purely with a node then the A and C node entries are zero equally if the error is on a link then the C node is zero while for an error associated with a turn all 3 fields are used Errors which are not associated with nodes e g errors in parameter inputs do not appear in the ERL list The error number uses the standard numbering system as listed in Appendix L e g all Warnings are in the range 1 99 all Serious Warnings in the range 101 199 etc etc The first 0 1 extra identifier field is used at the moment to distinguish whether the error is new value 1 or whether it has occurred in a previous ERL file in which case it is set to zero Thus an ERL file for a previous run of SATNET may be defined via a Namelist parameter FILERL input under amp OPTION in the network dat file and the errors listed in the new ERL file are compared to those in the old ERL in order to identify an exact match The second numerical identifier field is also used in association with a matching entry in an input ERL file but in this case the value is simply copied directly from the value in the
177. g algorithms are based on repeating a number of very simple steps a very large number of times any reduction in the basic step sequence no matter how silly it appears may lead to not insignificant reductions in CPU time 15 166 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 19 00 0 0 5120257 Apr 15 Section 15 Thus in the aggregate tree building algorithm based on dEsopo Pape see Appendix T we find empirically that splitting the algorithm into three distinct stages saves a small amount of time Specifically the stages are 1 Construct the minimum cost paths from the origin zone to all connected nodes Since we know that all the connected nodes must be added to the loose end table we can do away with that test 2 Carry on tree building through all real links but ignore all out bound centroid connectors to destination zones 3 For each destination zone consider all entry centroid connectors and choose the minimum cost alternative Once again we avoid any tests as to whether a minimum cost link requires a loose end table entry The reason that this 3 stage process appears to reduce CPU time for aggregate networks but not necessarily for normal networks is probably associated with the fact that aggregate networks contain a much higher proportion of zones and centroid connectors than normal networks see 15 56 2 above Eliminating Zero flow Links If we know in advance that certain links are
178. ggregate summary statistics by separate user class only for TOTAL FLOWS Worked Example A worked example is provided in the Test Network menu option 4 that will run the SATURN Epsom network for two scenarios without with development run SATSTAT to extract the summary statistics and open MS Excel using a Workspace and import the two SATSTAT output CSV files The SATURN files are located in the sub directory called TEST DEMO SATSTAT There are two sample networks a reference case called EPSOM98AXX DAT and a development scenario called EPSOM98RXX DAT Below we step through the process rather than running it all automatically Running SATSTAT in SATWIN The SATSTAT module is selected for running in the usual fashion as shown below for SATWIN11 from the Home tab we can select SATSTAT 15 123 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 4 EATUR Launch Cada P aoe 9 of eB X r H Home atrix Operations Post Assignment Viewers Conversion Advanced Versions magiel Tools Support Seam p S o9 P3P1X 4 Gs MXM1 Eo Gis 7 ENATCH MC SATLOOK MC SATOFF s Ao MMX io a PIKDUMP I SATUFO MC p X SATURN SATNET PMAKE SATALL SATSIM SATSTAT an MC ig SARDB sicopt E C Users SWAI2000 AppData Local Atkins SATWIN Model Default Test Model SATURN version 11 3 03 Level NAA Unsaved Task Description Module Parameters Executed Model Folder Program Folder
179. gh strictly speaking only for those nodes which lie on the interpolated path WARNING If two successive nodes to be interpolated are some distance from one another and there are multiple possible routes interpolation may not necessarily find your desired route the solution in this case is to define nodes which are much nearer together and for which the route to be interpolated is unambiguous Currently interpolated routes may be defined within the following programs SATNET to define bus routes See note 5 6 9 2 SATCH to define a spline of links along which flows are to be cordoned P1X to define bus routes joy rides and GIS alphanumeric link names Select Link Analysis SLA Select Link Analysis is a general term which refers to the identification of specific routes and or trips assigned to selected links where in this context links may refer to either roads or turns or centroid connectors or even nodes and the calculation of various properties associated with those trips Thus the analysis may identify for example the O D pairs which use a particular link the fraction of trips from each O D on a link the flows on all other links from the selected trips Other forms of analysis are of course feasible However the central element in select link analysis is the ability to trace the routes generated during the assignment process and to select those that satisfy a partic
180. gher 15 64 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 27 2 1 15 27 3 5120257 Apr 15 Section 15 distances so that the true average distance may also be greater or less than a skimmed tree The problem becomes more acute with quantities such as tolls which are much more off or on Thus if an O D pair uses two routes one of which is tolled and the other is not then it is somewhat hit or miss whether the single skimmed route gives zero toll or the full toll WARNING Skimming O D data from single path trees may therefore produce unreliable or misleading results The only quantity which may be skimmed absolutely unambiguously from say the minimum cost tree is cost itself In fact the only arguable advantage to skimming a tree as opposed to skimming a forest is that it is much faster only one tree needs to be built per origin as opposed to a forest skim where separate trees have to be built for each Frank Wolfe iteration e g it may be 50 or 10 times more time consuming Cumulative link node skims may also be obtained for individual links using the tree building option within SATDB in this case a distance skim for example would be the summed distance from the origin to the end of a link Similarly in P1X time and distance skims are automatically accumulated for O D trees plotted continuously there Default O D Costs In the event that a particular o d pair is not connected for e
181. ght hand drive instead of clockwise More serious problems might arise with junction types and or control strategies which are radically different from those used in the U K or more accurately cannot be represented properly by SATURN Output differences include writing right hand rather than left hand etc in messages and in annotating on the opposite i e correct side of the links in graphical displays where it is very important to have LEFTDR set correctly 15 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 8 15 8 1 5120257 Apr 15 Section 15 Using SATURN as a Conventional Assignment Model Buffer only networks As mentioned in Section 5 2 it is possible in the limit to use SATURN as a conventional assignment model by defining a network which consists entirely of a buffer network with no simulation nodes In such a case one would use SATNET to build a network file and SATEASY to carry out the assignment Given that there are no simulation nodes there is no necessity to use the simulation stage SATSIM and the assignment obtained from one execution of SATEASY is a convergent solution within the limit of the convergence parameters set Note that one could also use SATALL instead of SATEASY it carries out the identical assignment procedures and is recommended There are a number of reasons why one might wish to use SATURN in this way For example users might wish to model large
182. gregation the overall reductions for full runs are less spectacular than those demonstrated for pure assignment sub models above Five of the above networks were selected as identified with suffixes 1 5 to compare the overall runtimes for the full SATURN assignment using the four Frank Wolfe based assignment techniques currently available 5120257 Apr 15 15 169 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 Standard Frank Wolfe FW Multi Core Frank Wolfe Frank Wolfe with Network Aggregation technique and Multi Core Frank Wolfe with Network Aggregation technique The assignments were undertaken on the same desktop PC with up to four cores available to the software package The three main elements of the SATURN assignment are Path building and loading with fixed flow delay relationships assignment Updating the flow delay relationships representing vehicle interactions at modelled junctions simulation and Re estimation of the final paths and costs for skimming SAVEIT if selected The first and third elements are multi threaded whilst the simulation remains a sequential process Consequently the reductions in CPU time arising from using both network aggregation and multi core processes do not directly translate into the same proportional reduction in total CPU time Figure 15 15 presents the total CPU times for the FW algorith
183. hange formats are mostly associated with the ability to import data from other suites of programs with formats which do not coincide with those of SATURN Another example of the same basic principle is the parameter XYFORM used by SATNET see 6 3 4 lt should also be stressed that very often data may be read in a variety of forms provided that it appears within the column boundaries set and that therefore the formats specified within the Manual may not need to be absolutely strictly adhered to For example the format specified in order to read in the power for a buffer link speed flow is specified in Section 6 6 as FORMAT F5 1 implying that a single digit appears after the decimal point and that the decimal place must appear in column 39 In practice since FORTRAN compilers are forgiving in terms of input formats the decimal point may appear in any column with any number of digits following provided that the whole input appears in columns 36 40 Thus inputs of 3 3 0 3 123 will all be correctly read In addition certain inputs which are specified as Integers e g link times and or speeds with buffer link records may generally have decimal places included again with the proviso that the full input appears within the strict column limits Turning Flows at Buffer Nodes Although SATURN does not explicitly differentiate between different exit turning movements from a buffer link in calculating minimum cost routes unl
184. he increment is reduced so as to go only halfway to capacity In order to minimise any problems of noise in the two simulations if we are looking at two very similar flows any errors in delay calculations will be magnified we convert the value of NUC applied at signalised junctions to a large value In particular this has proved to be essential for junctions with very short signal phases and or X turns lf for whatever reason a node does not converge to the required limits see 8 3 2 even with any changes to NUC etc its convergence is judged to be poor and rather than permit any noise to creep into the calculations its MECC values are calculated using its separable cost flow curve and equation 15 15 above This is probably an underestimate of the total MECC since it exclude any interactions with other turns at that junction but this is felt to be preferable to introducing random errors In most networks the number of poorly converged nodes is probably well under 1 A higher percentage of poorly converged nodes may be an indication of slightly dodgy coding practice As an example of belt n braces and to cope with various noise problems which empirically are observed to occur even with all the above rules for priority and signalised junctions whenever both positive and negative increments are feasible we carry out two increments both plus and minus 1 pcu and take the minimum of the two MECC v
185. he main reason for introducing code numbers is to increase flexibility without a massive increase in programming effort particularly since certain data arrays are optional whereas others are mandatory Thus free flow travel times are always defined whereas the link flows for user class 4 may not be A full list of the Dirck Access codes used within a particular network UFS etc file may be listed interactively using the auxiliary program DALOOK or partial lists generated by P1X etc See also Appendix J for a full list Each array has a short title associated with it which specifies its contents these titles are defined in SATNET either as default text or as read from an optional supplementary file SATTIT DAT which also gives very useful general information about how DA codes are used Note that not all DA arrays will necessarily be useful to users for example the arrays containing packed data will be largely unintelligible but see 11 10 6 An explanation of the specific codes relevant to capacities is given in Section 8 9 5 and to times and delays in Section 17 10 See also Appendix J for a full list Creating your own DA codes in SATDB Users may add their own data to ufs files via SATDB referenced by a DA code of their choosing see 11 10 12 but care must be used not to over write existing essential DA codes This may sometimes lead to problems if the user selects a DA code for output which is available in that particul
186. he power n may then be determined by the equation n R R 1 B B 1 1 where O F C R log R R 1 P _ 1 F C R R log R 1 R S 8 R S S N B lim R log R R 1 1 and log above refers to the natural log 5120257 Apr 15 15 22 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 Our thanks are due to Yazid Arezki for working out the above formula thus confirming earlier numerical values calculated by Devon County Council In previous versions of the manual a set of calculated values of n for standard UK road classifications were provided in a Table often referred to as Table 15 9 with a shorthand description of each road type With the release of 10 9 24 the table was withdrawn as its inclusion was only intended to illustrate a range of typical values of N which may result using the formulae above from piece wise linear curves The values used in the table were Originally taken from COBA data sets of circa 1990 and were not in any sense recommended as up to date values for different road types In practice however users were applying the Table 15 9 curves without undertaking the necessary critical review required for their specific application To assist users an illustrative comparison of a typical COBA piece wise curve and the equivalent SATURN Power curve is provided overleaf in Figure 15 2 The data
187. hich have been converted to FCF operation may be viewed within P1X in several different ways Firstly they may be selected such that either only those nodes that have been converted are displayed or vice versa See 11 6 5 3 Secondly they may be assigned a numerical node data attribute 1 for converted to FCF O for not and displayed as node data within P1X network plots and or processed as a node data column within SATDB See 11 6 5 1 and or 11 10 5 Finally the standard print listing of node properties includes a line to indicate FCF operation for that node Simulation Buffer Transformation SBT Conversion to a Buffer Network The second method to reduce simulation based noise in an intermediate network band is to convert that band from simulation into a pure buffer network format with 15 4 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 1 8 5120257 Apr 15 Section 15 the inner segment remaining as simulation So in this case we will still have the traditional simulation buffer doughnut but with an extended buffer component We refer to this method as SBT Simulation to Buffer Transformation The SBT transformation may be accomplished by a combination of applications of SATCH SATBUF and SATCCS 12 1 15 8 2 and 15 8 3 respectively plus some text file editing to produce a suitably updated network dat file Thus assuming that we start from old_base ufs we proceed as foll
188. i e TxCij AAD as referred to in Section 7 5 5 Running SATURN in Parallel From SATURN v10 7 onwards a new feature was introduced that enabled users to take advantage of desktop PCs with more than one core and or processor This was intended as stop gap measure until development work on modifying the SATURN source code to access more than one core was completed during early 2009 Subsequent testing has demonstrated that the process is also compatible SATURN Multi Core and enables the maximum use of all the cores available The software was developed in response to a need to reduce runtimes for demand models where there is a requirement to undertake independent highway assignments by time period e g separate morning peak hour inter peak hour and evening peak hour models and to subsequent skim various permutations of travel costs and or demand for use in WebTAG based compliant models The recent advances in PC based desktop hardware has resulted in Intel based Core2Duo Nahlem Sandy Bridge chips becoming the norm amongst others and the existing methods of using SATURN to undertake tasks sequentially does not utilise any of the other cores available as illustrated below in Figure 15 6 and Figure 15 7 15 138 SATURN MANUAL V11 3 SATURN Special Options and Facilities Figure 15 6 Traditional Sequential Operation NNN NN A a A RN NN E E E E E E E EE E E E E POPC CCCP Cee eee E o Hi E E
189. ical data needs to be in fixed fields or sets of columns with a specific number of decimal places etc See Section 2 8 1 These are specified by format statements set within the program but which as explained here may also be altered by the user An example taken from the buffer network data input to SATNET see 6 6 Is given below Thus the first line specifies a buffer link from node 23 to node 22 in the standard format The line FORMAT 8F7 1 requests a new format the basic change being that the 3F7 1 implies that the three input fields following the A node and B node occupy 7 columns with 1 decimal place as demonstrated by the next data line for link 20 to 21 A line with characters FORMAT in columns 1 to 6 but blank thereafter causes the format to revert to its default 23 22 28 56 2500 2 1000 2 19 125 FORMAT 3F7 1 2X 1I1 A1 1X F5 0 F5 1 2X 13 20 21 28 1 56 1 2500 2 2 1000 2 19 125 FORMAT 20 21 28 56 2500 2 1000 2 19 125 In principle the change of format facility could be applied almost anywhere in practice it has only been programmed in a very few places including the buffer network inputs illustrated above In this case it has been done to make the data generated under the SATBUF conversion procedure see 15 8 2 accessible to SATNET Further extensions are planned 15 87 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 36 5120257 Apr 15 Section 15 The advantages of being able to c
190. ically if we wish to interpolate a path from node A to node Z we first work out the angle from A to Z then the angles from A to all its exit nodes B B2 and choose the B node whose exit angle is nearest to the A Z angle The procedure is then repeated by taking the angle from B to Z and choosing the nearest exit C Exits more than 90 from the desired direction are excluded it is therefore possible for the algorithm to become stuck if there are no exits within 90 In these cases the user will need to define more nodes within the path Alternatively post 10 9 an alternative interpolation algorithm has been introduced which finds the minimum distance route between A and Z if the first method fails This requires that a PARAM parameter MINDER is set TRUE 15 42 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 19 5120257 Apr 15 Section 15 Depending on the particular application the interpolated nodes may either only use real links in the sense that one way links are only used in one direction or non directional links This facility is particularly useful in defining bus routes not only in terms of reducing the amount of data to be coded but also because the route definitions do not need to be altered if the network is changed so that nodes are inserted and or removed from the original network Note however that in order to use this facility node co ordinates MUST be defined althou
191. ich is stored in a SATDB data base column which in turn may be read in from an external ascii file N B This option is only 15 65 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 available when SATLOOK is accessed via P1X and therefore SATDB may be accessed as well see 11 11 19 if a second network file is defined which is topologically identical to the first then a DA array from that file may also be nominated This enables one to e g skim average times on network 1 paths based on the times calculated in network 2 new in SATURN 10 1 In principle therefore it should be possible to set up properties such as fuel consumption or accident rates per link and skim them in order to create O D matrices of fuel consumption or accident rates In addition there are a number of sub options to modify the precise definition of certain skimmed quantities For example penalty times inout under 44444 may be optionally included or excluded extra time components associated with specific user vehicle classes under CLICKS may be in excluded and times distances on centroid connectors may be deliberately excluded XCCSK see 15 41 5 Note that a forest skim is only possible with SAVEIT T and also since it involves building and skimming one tree per iteration within the SAVEIT assignment it may take considerably more cpu time than skimming a tree However the results obtained will general
192. icts the AUTOZ option to pure simulation networks without a buffer network AUTOX and AUTOZ can both be selected at the same time and in fact the most useful case for applying both is the case of coding a single simulation junction as they remove the need to code ANY external simulation nodes or zones An example of coding a 4 way junction node 44 as illustrated in Section 16 1 is given in full below The coding implies that nodes 43 55 45 and 16 are external nodes each one of which is connected to an external zone also numbered 43 55 45 and 16 Note that the AUTOX option infers that the link 44 43 does not exist i e is one way from 43 to 44 since there are no turns coded as entering it and that the time and distance on link 44 45 will be 7 seconds and 100 metres Equally under AUTOZ zone 43 is entry or origin only while zone 45 is exit or destination only amp OPTION amp END NODE 44 CODED ALL ITS OWN amp PARAM AUTOX T AUTOZ T amp END 11111 1 1 1600X 2 2 15 31 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 13 5120257 Apr 15 Section 15 300 1400 11 3000 12 1200 22 220 1400 1 2 6 45 43 16 45 4 4 0 4 45 Supplementary Data for Simulation Links Using Buffer Network Inputs In general all the necessary data for links in the simulation network is defined within the 11111 data cards described in 6 4 e g the link travel time link distance and number of
193. ied out by a procedure i e bat file Known as SATMECC which in fact makes use of special procedures within SATLOOK The procedure outputs an ascii file details below 15 50 8 with an extension mec SATMECC was first introduced in 10 8 in 2007 and was developed with the financial support advice and technical co operation of GMPTE Greater Manchester Public Transport Executive and GMTU Greater Manchester Transportation Unit whose inputs are gratefully acknowledged Marginal Cost vrs Marginal Time Generalised cost is normally a weighted sum of time distance and other components such as tolls see 7 11 1 but of these only time is directly atfected by flows adding an extra pcu has no impact on link distance for example 15 132 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 50 3 5120257 Apr 15 Section 15 Therefore marginal cost is effectively equivalent to marginal time with a value of time factor i e PPM to convert marginal time into marginal cost in exactly the same way that time is converted to cost We note briefly at this point and in more detail later 15 50 5 that the value of time may differ between different user classes and that we may distinguish marginal cost by user class Within SATMECC outputs are always expressed in terms of marginal time in units of seconds pcu and it is up to the user to convert to marginal cost if and when desired Indeed it would probably be
194. ieved by the main simulation assignment loops such that the convergence in the main and SAVEIT assignments will be roughly comparable Prior to 11 1 UNCRTS was set equal to the final value of UNCRTS set during the assignment proper under AUTONA note 4 9 5 4 and which is generally a lower value than the GAP this could therefore lead to extremely long SAVEIT assignments for no appreciable gain in overall accuracy In addition to improve convergence SATURN also automatically sets PARTAN assignment under SAVEIT for single user classes and allows PARTAN as an option for MUC SAVEIT assignments via a parameter SPARTA See 7 11 7 and 15 57 6 Note that a side benefit of using PARTAN SPARTA is that by reducing the number of Frank Wolfe iterations required to produce a SAVEIT solution all subsequent analysis steps that use UFC files e g SATPIJA SLA etc will become correspondingly faster 15 54 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 23 5 5120257 Apr 15 Section 15 SATUFC Re creating UFC files A ufc file may also be created after the original run of SATALL using a procedure SATUFC introduced in SATURN 10 6 Basically SATUFC reads a ufs file and extracts the necessary information to carry out a SAVEIT style assignment with the added proviso that the value of NITA_S can be set as a purely numerical value on the command line E g SATUFC net 30 will produce an output file net ufc base
195. igned to time and distance Thus if PPK were near zero implying that distance is not very important in choosing minimum cost routes and an O D pair is assigned to two routes one with short distance and one with long then the skimmed distance could be anywhere between the minimum and maximum distances depending on the essentially arbitrary split between the two routes On the other hand the time skims in this situation would be far more stable since time would be effectively equal to cost and the costs on the two alternative routes would be equal Conversely if PPM is small then distance skims will be stable and time skims more variable Note therefore that different user classes which have different values of PPM and PPK may well behave differently For assignments based on Frank Wolfe as opposed to OBA calculating a minimum cost matrix requires one tree build operation per origin skimming 15 70 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 27 7 5120257 Apr 15 Section 15 an average matrix from a forest requires one tree build operation per origin per assignment iteration Hence it may require 25 50 100 etc times more cpu time depending on the value of NITA_S For large networks this time may be significant Note that this does not apply to OBA since skimming under OBA requires only a single pass see 22 5 6 Skimming Costs Using Bat Files E g SATCOST bat A number of useful standard bat file
196. ike the simulation network when the O D trips are assigned to paths through the buffer network they do implicitly go through turns and the resulting turn flows may optionally be saved To calculate and store buffer turn flows you must have both parameters SAVEIT and REFFUB which if you think about has a rational explanation as TRUE on entry to SATALL the facility is not available in SATEASY The turning flows are calculated by carrying out a final full assignment using the iteration costs stored on the ufc files See 15 23 and the resulting flows stored in DA array 4953 on the output ufs file These may subsequently be accessed using option 2 look at individual buffer nodes within SATLOOK 11 11 2 Note the following points 1 Bus routes through the buffer network clearly also make turns if there are any such bus routes their pcu turn flows are calculated within SATNET and stored in DA array 943 These are then added to the assigned flows in 4953 which therefore contains total pcu flows 2 The same treatment is not applied to pre loaded flows but see note 4 below 3 In multiple user class assignment all user classes are combined together in array 4953 4 Since as explained in 15 23 the routes re calculated via SAVEIT may be only an approximation to the true routes used in the assignment due to the effects of DIDDLE or KOMBI for example the turning flows are furnessed so that the total exit and entry flows
197. ill include the new flows etc If you wish to retain separate ufs files from each step it will be necessary to take a copy of each output ufs file with clearly different names The main advantage of using the re start facility apart from being able to skip one execution of SATNET is that the new sequence starts with the flow delay curves and simulation profiles from the previous run In the former sense RESTART is 15 9 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 5 15 5 1 5120257 Apr 15 Section 15 therefore very similar to the use of UPDATE within SATNET although the use of old simulation profiles is exclusive to RESTART If the new trip matrix is not much different from the old then the final flow delay curves etc will not be much different either Hence by starting with good approximations the overall number of assignment simulation loops can be sharply reduced section 22 2 2 contains further information on RESTART including its relationship with other similar kick start techniques Pre Loading Fixed Flows The Plod Option The pre load option was introduced at an early stage of SATURN development somewhat as a short term measure to deal with the problems of say assigning heavy lorries separately from other vehicles Indeed that particular application described in 15 5 1 has been largely superseded by the Multiple User Class Assignment option which is more general an
198. imes In effect network aggregation may be thought of as a form of pre tree building in other words before a minimum cost tree is built from a single origin a number of minimum cost sections are pre constructed from existing links which then allow the actual tree building to proceed with larger steps Thus if the node link sequence A B C D E F is repeated as a minimum cost segment for multiple origins then replacing it by a single aggregate link A F reduces CPU On the other hand if the aggregated link A B C X Y Z never features as part of a minimum cost path then its presence simply wastes CPU The trick therefore is to selectively aggregate good link sequences and to avoid the bad the current rather simple minded procedure must almost certainly be capable of improvement There may also well be more efficient methods for combining links together which are dependent on a particular set of link costs as opposed to the current network aggregation procedure which aggregates links without regard to costs lt may also be possible to eliminate a greater number of aggregated links prior to tree building than just removing the more expensive duplicates For example one may be able to apply a triangle rule which says that if nodes A B and C form a triangle and c A B c B C lt c A C then link AC may be disregarded in terms of tree building for that particular set of costs not necessarily universally An
199. in the hybrid network are aggregate the number of steps required and hence CPU will be reduced The concept of a hybrid network was first used in trip matrix cordoning where the event that distinguishes aggregate from normal links is the crossing of a cordon link either in bound or out bound See 12 1 4 note 13 It is planned to extend the principle to other areas of post assignment analysis such as SATPIJA and SLA We may also note that the concept of a hybrid network may be usefully combined with that of eliminating zero flow spider links prior to tree building and path tracing as explained above in 15 56 5 3 15 56 7 3 Banned and or Penalised Turns at Buffer Nodes 5120257 Apr 15 Section 15 Post release 11 1 it is possible to model banned and or penalised turning movements at buffer nodes provided that the node in question has been aggregated i e removed These are defined within the 44444 data section using the same formats etc as for simulation nodes See section 6 7 For example if a turn A B C in the buffer network is to be banned then if and when B is aggregated the aggregate link from A to C link A B plus link B C is not created If the turn is penalised then the aggregate link A C is created but any time A C is used during tree building then the necessary penalty is added to its cost The same principles apply if A C is part of longer aggregate links 15 172 SATURN MANUAL V1 1 3 SATURN Special Optio
200. in the same way that they appear on the screen but there may be certain restrictions Bitmap files are held by P1X in internal memory and the array thus used has dimensions 2001 by 2002 by default but may be increased by request which will normally cover the pixel dimensions set by the screen resolution However hard copy devices may well have pixel resolutions which exceed the above limits by considerable margins and therefore the program is unable to print full background bitmap images to such devices Currently only the upper half of the bmp file is printed so as to use as much as possible of the available memory a more permanent fix is currently being sought Note that a pre 10 6 problem whereby the network and the bmp file were printed with slightly different scales by 5 has been corrected 15 111 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 43 5 15 43 6 15 43 7 5120257 Apr 15 Section 15 There is however no problem in dumping the current plot plus bitmap display to a Omp output file or the clipboard and subsequently outputting to a printer but with some loss of resolution Bitmap backgrounds within Node Graphics In principle a bitmap image could equally well be used as the background to node graphics displays At the time of writing the necessary co ordinate transformations have not been worked out but it will happen soon Changing the Intensity of Bitmap displays
201. involve a relatively long and costly diversion Hence a distance skim along the used path should give 100 m for that O D pair If however on the very first all or nothing Frank Wolfe free flow assignment the initial assumption is that the signals are operating under capacity then that first assignment may optimistically severely over assign multiple O D trips along that link resulting in the downstream signals have a V C ratio of say 2 0 and a queuing delay LTP 60 of 30 minutes Hence an alternative route of 30 km at an average speed of 60 kph assuming time only assignment PPK 0 could be lower cost and that path would be selected on the second FW iteration and therefore become part of the final solution even if its contribution may have been diluted to say 1 by the end of the Frank Wolfe iterations Thus in terms of distance skims that path would add 0 01 30 000 300 m to the average distance so the skimmed distance would be 400 m not 100 In this case a small difference in flow has been magnified to produce a very much larger difference in outputs Frank Wolfe Assignment with Restricted Residual Flows There appear to be at least two alternative methods to minimize the impact of residual flows within Frank Wolfe assignment 1 Apply Frank Wolfe assignment as per normal but in any post assignment analysis of individual O D paths identify any which appear to be residual and remove them from the analysis or
202. ion nodes explicitly or to code zones at external simulation nodes which are cordon points Under AUTOX all nodes defined as simulation A nodes i e in cols 5 10 of Card Type 2 see Section 6 4 but not explicitly defined as simulation nodes themselves are automatically assumed to be external simulation nodes Thus if node 99 were defined as an A node as part of the definition of node 22 and not defined elsewhere then node 99 would be added as an external node with node 22 as an A node as well as being connected to any other nodes where it was included as an A node The properties of the link from 22 to 99 are inferred from data coded for 22 thus the travel time and distance are the same as those coded for link 99 22 but with default values of 100 metres and 7 seconds if 99 22 had zero capacity while if none of the turning movements coded at node 22 were into link 22 99 it is assumed that the direction 22 99 does not exist If however link 22 99 were included as part of the buffer network definition Section 6 6 then its time and distance as coded there will be used in preference to any default values as described above Alternatively since release 11 3 2 if default values are required i e the 100 metres and 7 seconds as above and SHANDY T then the default distance is calculated as the crow fly distance and the time is calculated assuming a default cruise speed of 51 42 KPH 32 mph lt should be stressed that the AUTOX option
203. is relatively short compared to a time unit and or the lane is shared For example if NUC is small and the basic time unit is say 15 seconds and the duration of a blocked phase is only 10 seconds then the simulated results may differ if the phase is entirely contained within a single 15 second time unit or if it overlaps two time units N B The differences between the two may not look that 15 37 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 large in some respects but they may not be negligible either For example if the calculated delays were 40 and 45 seconds the error of 5 seconds may be small compared to the differences between modelled and observed times on the other hand a sudden jump of 5 seconds may be relatively very important in terms of convergence between simulation and assignment Thus for signals with X turns we now recommend that NUC should be large enough so that the minimum length stage time is greater than three time units E g if LCY 100 seconds and the shortest stage time is 7 seconds then NUC should be at least 43 i e the basic time unit should be 7 3 seconds or 2 33 seconds and with LCY of 100 the value of NUC set should be equal to 100 2 33 or 43 rounded to the nearest integer Indeed there is a strong case for setting NUC LCY at signalised junctions with X turns so that the time unit corresponds to 1 second in order to achieve maximum r
204. ith 2 two way arms 2 one way inbound and two one way outbound would create 14 new links from 8 existing links i e we add 6 links and lose 1 node but the above rule says to go ahead regardless In fact this rule allows nodes with up to roughly 20 arms to be removed even if this seems totally counter intuitive empirically it saves CPU And hencc the default value of MAXSPA 15 noted above Note that there is a large degree of overlap between some of the steps Thus the nodes which are aggregated under steps 5 and 6 would also be picked up under step 7 but there may be a benefit to identifying the simplest structures and aggregating them first before eliminating the more complex node structures Note as well that the number of links per node is not fixed but potentially grows with each successive step Thus node A may have initially have 4 arms but if one 15 164 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 56 4 15 56 5 of its neighbouring nodes B is aggregated then A will have additional links added to all of B s other neighbours At the end of the process the aggregated network structure is stored within the ufn ufs files so that it may be optionally used within subsequent assignments and or analyses Implementation within SATALL Having created an aggregated network within SATNET the assignment procedure within SATALL may then be based on the aggregated network Thus the basic Frank Wolfe algo
205. ity used to calculate the V C ratio in equation Q 1 is taken after the weaving factor W has been applied to the saturation flow thus potentially increasing the delay If none of the above three conditions occurs then introducing a weave marker will have virtually no impact on travel times and hence on assignment Link capacity restraint speed flow curves are therefore highly recommended in conjunction with weave markers SATURN Namelist Parameters The following parameters may all be defined within the amp PARAM namelist parameters within a network dat file Section 6 3 to control the various options within weaving calculations WLMIN Minimum length for weaving in metres Lmin in Equation 15 2 WLMAX Maximum length for weaving in metres Lmax in Equation 15 2 PHILIP lf TRUE use Phil s formula Equation 15 13 STUART If True use Stuart s formula Equation 15 11 else use Equation 15 12 Note that the first two parameters are reals while the latter two are logicals The default values are respectively 300 metres 2000 metres False and True Thus if the weaving section were 300 metres or less the maximum reduction would be applied to saturation flows if it were more than 2000 metres than no reduction would apply Restrictions The weaving calculations may not yet be applied to all possible situations within SATURN Thus tt will not work with stochastic assignment SUZIE T It should h
206. l Computer PC The processor undertakes the tasks as specified by the Operating System usually a version of Windows and the software programs using the Operating System The processor may have a single or multiple cores with each core capable of running independently to provide additional computing power Most Desktop PCs will have at least two cores but four is becoming more common with higher end systems having six or more cores Cores and threads are often used interchangeably even though they are fundamentally different This has implications for the performance gains available from multi threaded applications Cores are physical hardware blocks in the central processor unit CPU that can run applications serially whereas threads arent physical but are software generated tasks that can be undertaken independently The computing power of each core is a fixed quantity available for use In day to day applications not all of the processing power available may be fully used if a software generated thread is paused or stopped whilst waiting for data so some of the processing 15 143 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 53 3 15 53 3 1 5120257 Apr 15 Section 15 power may be unused and wasted However running two threads on the same core enables the second thread to take advantage of this spare processing power whilst the first thread was waiting for data Whilst running two threads on a
207. lation to under estimate capacities The reasons for choosing 5 0 as a default in the first place are largely historical and arbitrary The reasons for not changing it since are a the fact that best values almost certainly vary from one to another hence it was made a junction specific parameter in later versions of SATURN and b setting the default to a more reasonable value might discourage users from deciding on more suitable values The same principles apply to the choice of GAPR and GAPM i e that they are first and foremost model parameters which should be interpreted only loosely as acceptable gaps However with priority junctions it is difficult to choose a single value of GAP which makes the dependence on ALL major flows linear since each major flow may have a different saturation flow Re constructing Assignment Routes The SAVEIT Option and UFC Files General Principles While the most important function of assignment is to obtain estimates of flows on links it is very often equally important to be able to analyse in detail the O D routes used to obtain those flows 15 49 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 Examples of analysis options which make use of O D routes include Building minimum cost routes in SATLOOK SATDB and P1X Repeating full loadings of complete trip matrices in SATDB 11 10 7 4 Select link assignments in SATDB and or PIX 15 19
208. lay capacity restraint relationships on out bound external simulation links such as A B above using exactly the same form of link flow delay curve as is applied to buffer links see Section 5 4 In order to do so the user must include A B within the 33333 data cards Note that for external links connected directly to cordon zones there is perhaps not much point in worrying about flow delay since all trips go to the external zone regardless of conditions on the link However the effect can be important on external links between the simulation and buffer networks as otherwise it could lead to a situation where there is effective capacity restraint in the simulation network and in the buffer network but not at their interface In addition if the AUTOX option is used to define external simulation nodes and links see 15 12 and the link in question is 1 way outbound A to B in the above example so that times and distances are given default values then these default values are over ridden by any data defined under the 33333 records 15 32 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 14 15 14 1 15 14 2 15 14 3 5120257 Apr 15 Section 15 Extra Link Data Knobs Introduction to Knobs SATURN allows a variable number of additional data items referred to as knobs to be input for each link buffer or simulation using the 33333 data records Section 6 6 and or separate input files t
209. le in the command line has an explicit extension CSV then it is assumed that the output data format will be CSV rather than fixed columns For example DEDUNNE mec aec Ge7 2508 SSi would dump demand flows for simulation turns to a CSV formatted file net csv 15 115 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 46 2 15 47 15 47 1 5120257 Apr 15 Section 15 P1XDUMP Dumping Data via P1X A very similar batch file to DBDUMP P1XDUMP dumps selected data to a text file but based on P1X internal codes rather than DA codes For example the command P1IXDUMP net flows txt 5 dumps the free flow speeds P1X internal code 5 from net ufs into a file flows txt See Appendix for a full list of codes To request a particular user class for a user class dependent variable Such as link flows the class is indicated by appending Un to the internal code for example P1IXDUMP net flow_uc4 txt 40U4 dumps the demand flow for user class 4 The options SL etc described above under DBDUMP apply equally under P1XDUMP CLICKS Variable Free Flow Speeds by User Class General Principles of CLICKS The CLICKS parameters represent a somewhat simplistic method to model the clearly evident fact that on say motorways heavy lorries travel at a lower speed than cars whether due to speed restrictions or to vehicle characteristics or both Setting a parameter CLICKS 2 100 signifies that
210. les by BarGera and others Proportionality requires that at any node A where there are more than one exit links that are on minimum cost paths to another node further downstream i e they represent parallel route segments with the same cost then the proportion of trips using each segment exit link must be the same for all origins and or destinations Thus with reference to the example of two parallel links as described in Section 7 16 the 50 50 split between the two alternative path segments must be maintained for all origin and or destination flows Proportionality is thus only a statement of conditions which must hold it does not in itself provide an algorithm for achieving such a solution However there are certain assignment algorithms which have recently been developed which do generate proportional solutions but which have not reached the stage of finished products An alternative principle for specifying a unique set of path flows is that of entropy maximisation where we choose a set of path flows T which maximise the entropy measure see equation 13 2 in section 13 1 1 To a large extent as understand it proportionality and entropy maximisation generate the same solutions but there may be pathological situations where they differ To a certain extent the differences are academic since algorithms to solve for either are hard to come by 15 24 Alternative Link Costs and or Times for Tree Building 15 24 1 Intro
211. lso include the central simulation links and centroid connectors converted to buffer format but since the same links etc also appear in the new 11111 and 22222 data sets they will be ignored by SATNET under 33333 FCF vrs SBT The two methods described above FCF and SBT have common objectives that is to reduce simulation noise in areas far removed from a particular scheme where major changes would not be anticipated and to improve overall convergence and CPU They differ in the levels of aggregation applied within the intermediate region 15 5 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 2 5120257 Apr 15 Section 15 Thus FCF retains the same basic geometry in the intermediate region whereby each turning movement is still represented by a single link within the assignment network with a fixed cost flow curve and therefore in terms of route choice different turning movements from the same entry link influence route choice By contrast with BCF the distinction between different turns has been removed In addition the FCF formulation permits flow metering to be modelled whereas with SBT as with any buffer network there is no distinction modelled between demand and actual flows We may also note that to a first approximation a network with a FCF conversion gives the same results as the original simulation network In fact the first assignment after the FCF transformation should give identical results
212. ly a two field entry A Z will correctly identify a single simulation centroid connector from A to Z with the extra node B inferred 15 35 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 14 5 3 15 14 6 15 14 7 5120257 Apr 15 Section 15 Sound complicated Stick to wildcard definitions Wildcard Inputs In addition KNOBS data read from an external KNOBS file FILKNB may post 10 8 define links using a wildcard principle whereby if an A node zone is defined but the B node columns are left blank or zero then the program assumes that the KNOBS data applies to all links out of the A node zone Similarly if the A node entry is blank or zero but the B node is defined it applies the data to all entry links In particular this facility is designed to enable users to set entry exit tolls on Zones without having to precisely specify each individual centroid connector to or from a zone The wildcard principle applies to all forms of zones and centroid connectors i e not only zones connected to buffer nodes but also zones which are connected to internal simulation links for which more explicit data inputs see above are easy to get wrong Note the wildcard principle may also be used to define all entries exits from a buffer node although not from a simulation node In all three cases if data is not set for a particular assignment link that value defaults to zero Thus in the case of a separate fil
213. ly soeaking be more accurate and are recommended for use in matrix based evaluation such as TUBA In particular a forest skimmed matrix satisfies the condition but see 15 27 5 below that DTS T gt VS 1J a where the left hand side of the equation represents the total say vehicle kms summed over ij pairs and the right hand side represents the same quantity summed over links Sj and Sa refer to the property being skimmed e g distance Note that some care needs to be exercised in the definition of Va in the above equation since it must be 1 the link flows from the trip matrix itself e g excluding any fixed link flows and 2 demand as opposed to actual flows We return to this point in the following section We may also note that forest and tree skims will give identical results for O D pairs where the assignment has only generated a single route Typically this occurs for very near O D pairs or for very uncongested sections of the network For further information on SAVEIT and forests please refer to sections 15 23 and 15 26 We also note one additional caveat with forest skims which is that since the path flows generated by a Wardrop Equilibrium assignment are not strictly speaking unique see 7 1 6 neither are skims taken over those paths see 15 23 8 The example given in 7 1 6 as to which origin s pay tolls illustrates the problem although in practice the problem is much more likely to be that the model shows
214. m combined with the NA and or Multi core techniques using the five SATURN models The total CPU time is normalised with respect to the standard FW algorithm The results show that all three techniques using either Multi Core and or Network Aggregation are at least twice as fast as the existing standard FW algorithm for all five models and in the best case found virtually 20 times faster The reductions in CPU expenditure achieved by the Multi Core algorithm or the Network aggregation on its own are broadly comparable with CPU time reducing by a factor of 2 to 2 5 for Model 5 increasing to factors between 4 and 5 for Model 1 In most cases aggregating the network before assignment is more efficient than distributing the original network across more than one CPU core the exception is the very large Model 3 network 15 170 SATURN MANUAL V11 3 SATURN Special Options and Facilities Figure 15 15 CPU Time by Algorithm Normalised to Standard FW Model 5 Model 4 n a n 0 15 Model 3 _ o ee Model 1 7 0 18 0 00 0 10 0 20 0 30 0 40 0 50 E Multi Core FW mFW with NA E Multi Core FW with NA As expected creating a multi core version of the network aggregation provides a substantial multiplicative reduction in CPU time In all cases Multi Core FW with NA reduces the CPU expenditure by factors of between 3 Model 5 and 20 Model 1 The overall performance gain is principally determined by the
215. mary Spreadsheet files we select the Summary worksheet and press the Import CSV button to bring up the Windows File Open dialogue box 5120257 Apr 15 15 126 Section 15 SATURN MANUAL V11 3 SATURN Special Options and Facilities ti Microsoft Excel Summary Report v3 00 xls iB File Edit View Insert Format Tools Data Window Help MAW a MEME UE a FEN eee a eee 9 0 00 00 0 HA0002 SATURN Support lJWright Atkins Date Created 30 05 05 version 2 00 0 E Summary for REF J Loops N Select the CSV File Q pai eres Look in Demo Satstat v 11I X amp E Tools gt BL EPSOMOBAXX CSY Statistics Summary Results CJ LJ EPSOM9BRXX CSY My Recent Matrix totals pcus hr Documents A4 Transient Queues Total pcus lt Proportion carried over gt 2 Over Capacity Queues pcus 56 lt Proportion carried over gt 63 Link Cruise Times Total pcu hrs lt Proportion carried over gt Total Travel Times Total pcu hrs My Documents lt Proportion carried over gt _83 Travel Distance Total pcu kms e 56 lt Proportion carried over gt Average Speed Overall km h My Computer lt Ratio gt Delay Total peu hrs e Delay Vehicle mins veh My Network Congestion Index mins veh km Places Files of type csv files csv Average Trip Length km Desktop File name
216. matrices capacities etc are defined in units of pcu hr into vehicles VCPCU is useful in circumstances such as vehicle emissions when it is more natural to deal with parameters per vehicle rather than per pcu It is also used in the calculation of toll revenues see 20 4 1 which are paid by vehicle rather than by pcu Post 10 7 P1X has an option to annotate individual user class link flows in veh hr instead of pcus hr by factoring the assigned flows by 1 VCPCU However it is more difficult to apply the same option to e g total flows where some of its components passq flows etc may not be unambiguously identified with a single user or vehicle class and hence pcu factor Note that by default all VCPCU factors equal 1 0 in which case it has no direct effect on any SATURN outputs Interpolating Routes Several programs require that routes e g bus routes joy ride routes etc be defined as a sequence of consecutive nodes For long routes this can be laborious and therefore a simpler method is available if node co ordinates have been defined whereby the user defines the first and last nodes and the program works out the sequence of nodes which most closely approximates to a straight line or crow fly path between the two nodes The principle can be extended to the case where a route is defined by more than two nodes the first and last plus any intermediate nodes where there is a decided kink in the route More specif
217. mber of different networks for example a do minimum and a do something network which have some different node numbers and therefore different sequential numbers In particular a new option in P1X see 11 4 2 allows for a file to be created containing the names and sequential number based on a union of all nodes lf your network has more than 9999 sequential map numbers it cannot be used by COBA in its current form and you re in deep doodah Try a cordon maybe Bitmaps within SATURN General Principles Bitmaps are used as inputs within SATURN to provide a background to network plots within P1X see 11 3 6 Thus instead of a blank i e white screen background an image obtained from a bmp file is used and the network plot is over written upon it An example from the central area of York is shown below Note that in this case the network window as nominated by P1X is larger than the area covered by the bitmap so that there is a blank surround to the bitmap Had the bitmap covered a wider region than the network window then the appropriate region of the bitmap would have been selected and suitably expanded Thus a very useful property of the bitmap displays is that they move with the network window 15 108 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 eS d i Sogi Within this particular context bitmap files must be of either bmp
218. me conventions for capacity indices and vehicle classes KLUNK 1 Disaggregate by Capacity Index To input variable values of CLICKS by vehicle class under KLUNK 1 the user must either a prepare a text file formatted as below and define its file oathname via the text parameter FILVSD input under amp PARAM in the network dat file or b include extra records within the 33333 buffer data new with 10 9 15 47 2 2 FILVSD File Input 5120257 Apr 15 Section 15 The file must contain one record for each Capacity Index for which CLICKS values are required with the first entry field containing the integer Index and the following values containing the real maximum speeds for Vehicle Classes 1 2 3 The format is essentially free each item must be separated by either a space or a comma from its neighbours i e CSV is acceptable All values for 15 118 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities Capacity Indices not included in the file default to zero i e maximum speeds are not applicable as do missing or zero values per Vehicle Class as input For example if capacity index 1 refers to a road type where vehicle classes 1 and 2 have normal link dependent speed flow curves but vehicle class 3 HGVs maybe has an upper speed limit of 88 kph the relevant CSV formatted record would read 1 0 0 88 and the maximum speed of 88 kph would then apply to all user classes associated with vehi
219. mment cards indicated by a in column 1 Any such records are ignored and the next record read This complements the use of in the namelist input conventions to indicate comments at the end of a line see Appendix A This convention was first introduced in SATURN 9 1 5120257 Apr 15 15 75 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 30 5120257 Apr 15 Section 15 For network data files comment cards are particularly useful for e g identifying specific nodes inserting comments when changes are made impresses the QA boyos or for editing out previous coding In practice the convention may not be 100 fool proof as the new rule has meant changing every single read statement to check for the almost certainly some will have been overlooked It should be fairly obvious when this happens most likely the program will crash so the obvious solution is a remove the comment card and b politely alert your friendly SATURN agent The same convention applies to other input ASCII files in particular key files may have comment lines inserted as may the standard graphics system file graf dat Blank lines in input data files are generally soeaking handled in the same way as comment cards i e if read they are ignored and the next record read in its place If on the other hand they are allowed as input numerical records see below they are interpreted by FORTRAN a
220. more accurate to refer to MECT rather than MECC but we retain the more standard convention Marginal Cost Calculations Incremental Simulation MECC values per simulation turns are estimated by a carrying out a full simulation of the base to obtain both base delays and base flows per turn and b repeating a full simulation of the node with an additional small increment of flow AV e g 1 pcu added to the turn in question But see 15 50 6 for alternative procedures in selected circumstances The total value of MECC may be calculated as Equation 15 17 MECC gt V d 1 d B AV Where i represents a particular turning movement link at that junction including a V is the total demand flow for that turn AV is the increment of traffic to the current turn a either positive or negative di 1 is the simulated delay with the increment AV d B is the delay in the base simulation Notes 1 This definition excludes the current cost of link a i e the first term on the right hand side of 7 46 However it is not difficult to add this contribution later on as required 2 Strictly soeaking Equation 15 16 defines marginal time not cost since we use unweighted delays in units of seconds 3 This method can give both positive and negative values of MECC whereas the use of equations with separable cost flow curves can only yield non negative values Negative MECC values may seem counter intuitive but in
221. n that it jumps from a value of 2b max Lmin 1 gt 1 at L Lmax to 1 0 at L gt Lmax Recall that the maximum value of X is 3 0 at L lt Lmin Two alternatives have been suggested in addition to retaining the discontinuity i Reducing X by a constant amount throughout such that it goes smoothly to X Lmax 1 0 and is 1 0 beyond ii Assume that X L is a linear function between L Lmin and Lmax going from 3 0 down to 1 0 More specifically under assumption i we introduce a correction factor equal to the normal value of X at L Lmax less its desired value of 1 0 Equation 15 11 b C 2 0 Lis Hence the full formula for X L is 15 94 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities Equation 15 12 3 0 2 0 ai LsL Le L L X L 41 0 2 0 lt Lain lt Le lt Lina L 1 0 L gt L Method ii may be written Equation 15 13 3 0 Eat X L 1042 0 a bee Les Laax 1 0 bo Having established X by whatever method an alternative method for establishing the capacity reduction factor W is to use the formula as proposed by Philip Barrett of HKBR Equation 15 14 W100 22 Q w Which to a first approximation is the same as Equation 15 9 for small corrections but is less severe as the effect increases e g as Qw2 increases Thus whereas Equation 15 9 gives a maximum reduction minimum W of 0 5 Equation 15 13 gives 2 3 under the same co
222. n the form of physical cores or virtual threads available on most Intel AMD powered standard desktop PCs SATURN MULTI CORE is a separate low cost add on to the standard suite and may be accessed through an updated set of executables and system files The control of the multi threaded processors is automatically undertaken by the program and the Operating System Multi processor applications may be sub divided into two categories a those programs that allocate calculations to separate threads internally within the processor s and therefore need to be linked with certain routines compiled using IVF as opposed to Salford Fortran and b those where the allocation to separate threads is handled at the level of the batch file but the same basic program exe is used for each thread distributed processing as previously described in Section 15 52 Applications under a require distinct EXE files those under b require special bat files identified with the MC suffix In principle method a should be faster and more efficient than method b but on the other hand it requires specially compiled versions of the exe files whereas method b uses the standard exe s but with clever batch files Method a works by allocating tree building etc operations by origin between processors method b works at a much more aggregate level by allocating say calculations per user 15 141 SATURN MANUAL V1 1 3 SATURN Special
223. n 15 6 and is the default link flow as annotated by program P1X By contrast the ARRIVE FLOW or Downstream Flow as printed out by the FLOW DELAY tables and illustrated in Table 17 1 corresponds to the stop line flow YB above 15 40 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 16 2 15 17 15 17 1 5120257 Apr 15 Section 15 Simulation Link Exit Entry and or Upstream Downstream Flows The previous section has described how flow may exit the network at the upstream end of a simulation link and equally enter the network at the downstream end of a simulation link using centroid connectors It is also possible for flows to exit enter at either the upstream or the downstream end of simulation links even if they are not explicitly connected to zones This possibility arises with bus routes which may originate terminate at either end of simulation links dependent on UPBUS see 6 9 2 It may also arise less obviously with either pre loaded or PASSQ flows see 15 5 and 17 3 1 respectively where the rule flow in equals flow out may be violated Thus in effect all simulation links are potentially bridged by exit entry links although only those with explicit centroid connectors are shown as such on e g P1X plots Please note that this possible ambiguity ONLY arises with links in the simulation network and not at all to links in the buffer network where there is only one possible definition
224. n a high performance desktop PC Typically the multi threaded applications reduced the overall model runtimes by up to 1 N where N was the number of physical cores available depending on the size and type of network and the assignment parameters used For example on a quad core machine the model runtimes on various test networks were reduced by up to a factor of four Note that all the tests were undertaken on the same HP XW8600 workstation 2 x Intel Xeon X5450 3GHz with 4Gb RAM running Windows XP 32 bit The processors provided eight physical cores with each core able to handle one thread each i e no Hyper threading option was available on these particular processors SATALL Multi threaded The performance gains available with the multi threaded version of SATALL are shown below in Figure 15 8 The overall reduction in the total CPU time for SATALL was reduced by up to 3 5 times on a Quad core PC With an extra fifth core available further reductions in model runtimes were achieved but with six or more cores the model runtimes marginally increased in this example 15 144 SATURN MANUAL V1 1 3 Special Options and Facilities SATURN Figure 15 8 Example of SATALL Performance Medium Size Network ma CPU Ratio h O _ 1Core 2Cores 3Cores 4Cores 5Cores 6Cores 7Cores 8Cores lt 3 z c a cD Sem O UO a eTe S N eTe c a x LLJ t e X in ea aa ee The assignment unde
225. n it Flow 2 will need to weave with traffic which is already on the motorway but wishes to take the next exit Flow 3 This will lead to a reduction in the capacity of the middle segment of the motorway if the fraction of traffic which weaves is high and or the distance between entry and exit is relatively short 15 91 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities Figure 15 4 Fig 2 7 from DMRB Vol 6 Sect 2 part 1 15 40 2 5120257 Apr 15 Section 15 Qnw non weaving flow Flow 1 Flow 4 Qwi major weaving flow greater of Flow 2 or Flow 3 Qwe2 minor weaving flow lesser of Flow 2 or Flow 3 Figure 2 7 Terms used in Weaving In these situations SATURN uses formulae derived from DMRB Design Manual for Roads and Bridges recommendations to reduce the saturation flow and hence the capacity of the link or links comprising the intermediate segment N B The treatment below only applies to links coded as part of the simulation network not buffer In addition tt need not apply only to motorways SATURN normally does not know whether a link is motorway or not although in practice the required geometry of entries and exits is most likely to occur with motorways In addition it may not be used if the assignment is based on either path based assignment OBA or multi core In principle it could but it hasn t been coded requests to DVV Basic Background Theory Paragra
226. n of penalties is always included under the definition of cost e g used to define minimum cost routes since it is an integral component of the fixed link costs Equally any extra travel times associated with specific user classes calculated using the CLICKS options 15 47 are also included by default N B CLICKS was only introduced in 10 6 On the other hand there will definitely be occasions when a user wishes to exclude 44444 penalties and or CLICKS in the definition of times Thus in the interactive menus used in P1X SATLOOK and SATDB to define time for tree building and or skimming there are toggle options to explicitly include or exclude CLICKS and or penalties In addition the include exclude default options may be user set using parameters USETP and CLICKY in the appropriate preferences files SATLOOKO dat etc Thus if USETP T then if time is selected it will include all 44444 time penalties for that user class similarly if CLICKY T then times defined according to CLICKS are used in preference to normal times Both parameters default to T Units of Time and Costs As explained in 7 11 1 SATURN conventionally expresses all costs as generalised time as opposed to generalised cost within the assignment procedures The same rule also applies by default to the analysis of the assignment via tree building etc although with 9 1 options have been introduced to allow costs to be defined in
227. n running multiple time periods using SATTPX 17 4 3 since in that case each time period has a unique filename e g neta netob netc etc emanating from a single data filename e g net dat The individual time period filenames will be automatically and correctly invoked if UPDATE T in net dat but no specific ufs filename e g net ufs is set The UPDATE option may be very usefully combined under either path based or origin based assignments with the WSTART option which adds additional information related to path flows and which improves the initial 15 8 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 4 5120257 Apr 15 Section 15 assignment even more than just having improved cost flow curves See 21 3 for further details Updating the Trip Matrix The Re start Facility The re start facility allows a user to carry out a full set of SATALL simulation assignment loops when the only difference between the current and a former run is in the trip matrix for example when SATWME2 is used to estimate successive trip matrices or when the assignment is part of an external demand supply procedure possibly using MX If there are any other differences at all apart from the trip matrix e g changes in PASSQ flows etc etc then a re start in SATALL is not appropriate Re start is effectively equivalent to UPDATE Section 15 3 the main distinction being that it is applied directly within SATAL
228. n the buffer network exceeds 5 digits then the first two fields occupy 9 columns each and the third which is zero by definition occupies 2 columns i e 0 in column 20 In general MECC values are printed with two decimal places with units of seconds although in some extreme cases there may not be sufficient width in the format to permit two decimal places in which case MECC is printed in an E format Running SATURN within DIADEM The DIADEM suite of programs has been created by Mott MacDonald under contract to the DfT to provide demand matrix calculations linked to various traffic assignment programs In particular Diadem has been linked with SATURN such that Diadem calculates vehicle trip matrices which SATURN may then assign See Section 7 4 5 for a discussion of the general VDM principles involved and for suggestions as to how to make the overall process more efficient Full documentation on Diadem and its linkages with SATURN are provided by the Diadem documentation Generally the procedures for running SATURN programs within Diadem are controlled by Diadem itself However there are various options within SATURN programs which may assist in achieving a well converged solution with minimal cpu and which either users may set themselves in their network dat files and or Diadem developers may incorporate within the internal control procedures It is highly recommended that Diadem users ensure that they are running the most up
229. n within SATALL with SIGOPT F has even less to recommend tt N B Optimising stage times in particular and or offsets may lead to significant improvements in the overall convergence of the assignment simulation loops See Section 9 1 5 NIPS On the other hand using the parameter NIPS to limit the number of times the signal and or offset optimisation within SATALL is called is STRONGLY recommended See 9 12 2 A value of 2 or 3 is recommended Preserving and Transferring New Stage Times Having created new stage times and or offsets by any of the above methods it is natural to wish to include that information within a network dat file The best way to do that is to use the Network Editing facilities within P1X and in particular the update option described in 11 9 13 2 and or rgs files as described in 11 9 14 Alternatively the batch procedure described in 15 31 6 has options to output an updated dat file automatically Once an updated dat file has been created you may wish to re run SATURN from scratch with the signals and or offsets fixed at their optimal values Before you do so be careful that parameters such as SIGOPT or SATOFF have all been turned off within the new dat file Also note that the from scratch results may not be identical to those previously obtained since the new run may follow a slightly different convergence path and wind up with slightly different results only with perfect convergence
230. named picture xyb which specifies the 4 corners of picture using the same coordinate system as that used by the network i e the co ordinates as used within the 55555 network data section and independent of XYUNIT 6 8 xyb files consist of a single record containing 4 real values in the following order 15 109 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 43 2 15 43 3 5120257 Apr 15 Section 15 XMIN the east west co ordinate of the lower left hand corner XMAX ditto for the upper right corner YMIN the north south co ordinate of the lower left hand corner YMAX ditto for the upper right corner Optionally a second record may be included which contains the intensity scaling factor to be applied for that particular bmp image see 15 43 6 Note that the units of XMIN etc should be the same as the units of the node X Y co ordinates as defined under the 55555 records in the original network dat file see 6 8 Thus if XYUNIT 10 0 so that the co ordinates are defined to the nearest 10 metres then XMIN etc should also be the nearest 10 metres However as noted in 15 43 2 we strongly recommend that all co ordinates are defined in units of metres to minimise confusion The xyb file may be most conveniently set up the user assuming that the information is known in advance through knowing the source of the image Alternatively if a bitmap is input into P1X with
231. nces for running SAT TUBA see 15 41 5 Coding Combined Buffer and Simulation Networks Problems may arise in coding a network which includes both a simulation and a buffer network in particular at the interface between the two The following points may help 1 The simulation network is coded in the normal way with external nodes defined at the edge of the network either explicitly within the 11111 data records or implicitly via AUTOX If the external nodes represent cordon or stub nodes where the network terminates then they would normally be connected to cordon zones i e Zones representing all trips entering or leaving the network at these points These zones should then be included within the 22222 data records or implicitly via AUTOZ The precise points of zonal connection will be at the external nodes as described in 16 6 2 Alternatively the external connection to the zone may be made via an external simulation link plus an isolated buffer node which is coded under the 33333 data records as described in 16 6 3 However this method is generally not recommended as it leads inter alia to the same problems with U turns as described in Section 16 6 4 and 18 9 2 However external simulation nodes may also represent points where the simulation network connects continuously into the buffer network and in this situation origin destination zones at the boundary may be connected either via the buffer or
232. nder DUTCH T The calculation of n then follows the equations as given in 15 9 3 where the additional parameters S S and C as given within the normal 33333 fields see 6 6 For the time being the option to directly calculate n from COBA 10 curves only applies to Default speed flow curves within the 33333 data records not to individual link records However there is no reason why it should not be extended to individual records and if no problems arise with the above method it will no doubt be included in the next release The use of Crow Fly Distances The SHANDY Option General Principles The SHANDY option set SHANDY TRUE in the input network dat file carries out the following two steps for every input distance for either a simulation or a buffer link Ifa positive value has been input it checks this against the crow fly distance calculated from the input XY co ordinates and prints a warning message WARNING 35 if they differ by more than 10 metres in absolute terms AND by more than 5 in relative terms 15 27 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 10 2 15 10 3 5120257 Apr 15 Section 15 Ifa zero or blank value has been input it substitutes the crow fly distance calculated from the input XY co ordinates and prints a warning message WARNING 25 Clearly these steps are only carried out for links where both the A node and the B node have been correctly assig
233. nditions A final extra rule is to set a minimum value on the capacity reducing effect of weaving traffic by requiring that say Equation 15 15 W gt W 0 75 Which or which combination of the above approaches is preferable is very much in the eye of the user There is very little empirical evidence to say that this equation is right and that is wrong what SATURN is doing is providing a set of approaches which have been proposed by experienced modellers and let the user decide And if the user has an alternative approach it should not be too difficult to include alternative formulae within the programs 15 40 4 Application within SATURN To apply capacity reductions due to weaving within SATURN users must a set various parameter values as used in the above equations strictly speaking 5120257 Apr 15 15 95 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 40 4 1 optional as default values are provided and b identify those links where weaving occurs Network Coding the W link marker We note first that a weaving section may consist of either a single link as illustrated in Figure 15 4 connecting the node with the on ramp to the node with the off ramp or less frequently a series of essentially one way links connecting the on and off nodes as illustrated in Figure 15 5 Link identification is accomplished by coding a W within the 4 colum
234. necessarily not apply to other algorithms such as OBA is that of residual paths A residual path is one which has been generated as a current best route on an early iteration of Frank Wolfe but which by the end of the algorithm is very much longer than the current best route but has not been totally removed from the final averaged solution Thus consider a situation where an O D pair has two alternative routes available a short route that goes through a signalised intersection and a long route without potential capacity restrictions At equilibrium the signals are under Capacity and incur relatively minor delays and the all or nothing solution with all O D flow going through the short route and none on the long route is the correct solution for this particular O D pair However it may have happened that on an early FW iteration most likely the second iteration following the initial all or nothing assignment to free flow routes the signals had become heavily over capacity due to the routes chosen by alternative OD pairs which later divert elsewhere and the minimum cost OD route for our particular O D pair went via the long route on that particular iteration But on all subsequent iterations the signals are never again as over saturated and the best O D route is always via the signals In this case the final path flow contribution from the long route as expressed by equation 7 2b will never be reduced to zero u
235. ned X Y co ordinates The option works by pre reading the co ordinate data under the 55555 cards before returning to read the simulation and or buffer link records Thus no interpolated co ordinates are available at this stage If there are no co ordinates input then the option is cancelled In addition if a GIS file is defined in the network data file via FILGIS and that file contains curved link data under 77777 then the crow fly distances as used to compare against input link distances SHANDY T are calculated point by point along the curved links rather than end to end directly See Appendix Z Note that this option may be usefully combined with the default speed flow curve facility described in Section 15 9 5 since the new distance is set BEFORE the speeds are substituted Thus the free flow time is obtained from a crow fly distance divided by the free flow speed At a minimum therefore a buffer link record need only contain an A node B node and a capacity index It is also an integral part of the PMAKE network building options see section 17 when new links are created A summary table comparing actual and crow fly distances is included near the end of the line printer output file from SATNET Correcting XYUNIT In addition an estimate is made of the correct value of XYUNIT by comparing crow fly distances as calculated from the node co ordinates with the input distances on the dat file and printed near the end
236. ng the updated signal settings N B This replaces similar options previously available under option 1 of the now discontinued program SATED An illustration of a typical sequence of programs is given below SATALL or SATEASY SATSIM Net1 UFS SATED P1X Net2 UFS SATALL Having re assigned and re simulated via SATALL the option of course exists to loop back through P1X in order to re optimise the signals subject to the caveats expressed in Section 15 31 1 The optimisation process may also be carried out at selected nodes only 11 9 13 2 15 79 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 31 3 5120257 Apr 15 Section 15 Alternatively a new batch procedure SIGOPT has been introduced in Release 10 8 16 to optimise stage times and or offsets and which effectively supersedes both SATED P1X in terms of stage times and SATOFF in terms of offsets described in detail in 15 31 6 Thus in the above diagram substitute SIGOPT for SATED P1X Stage Length Optimisation Algorithms Five basic algorithms to optimise stage green times are provided SATURN Equi saturation Webster Oo M Delay minimisation PO 5 SATURN Equi saturation Mark 2 D The first is the traditional algorithm provided for many years within SATURN the last is a recent modification thereof while the remaining three were first introduced in SATURN 9 2 having been converted from
237. nitial stages of an assignment should it is hoped discourage the build up of residual paths since as congestion builds up more slowly on early incremental assignments the correct O D pairs should be able to choose alternative routes avoiding locally congested links In particular the use of incremental assignment is potentially recommended to reduce residual paths during SAVEIT assignments 15 23 2 Set the Namelist parameter INKS_S 4 say in the network dat file Error Listing ERL Files Structure and Contents Version 10 9 17 contains a new feature Error Listing Files ERL which provide a list of the errors reported within SATNET ordered by node number s rather than in the order in which they are detected as they appear in the body of LPN files or sorted by error number as in the LPN summary statistics Thus at the end of SATNET a text file with the extension ERL is created which contains one record per error detected with the following data fields i A node li B node lil C node v A 0 1 identifier Extra field 1 iv Error number vi A second numerical identifier Extra field 2 vil The short text message associated with the error number 15 177 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 58 2 5120257 Apr 15 Section 15 A sample segment of a ERL file follows a OOS 102 hires saburakion slows pen lane di Erer widely AO 2 9 7 IO Opposin
238. nless unlikely a particular value of lambda equals 1 0 The creation of incorrect residual flows is an intrinsic property of the Frank Wolfe algorithm and is one of the reasons why its convergence rate slows drastically as it approaches convergence Apart from slowing down convergence residual flows may also have several other undesired consequences The Importance of Residual Flows The practical impact that residual flows may have on different forms of path analysis see the list in 15 23 1 can be extremely variable For example in Select Link Analysis if a link has a total flow of 1000 0 pcus hr of which 0 1 is based on 15 174 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 57 3 5120257 Apr 15 Section 15 residual flows then the differences between including or excluding the residual flows is arguably minimal On the other hand the impact of a small residual flow may be considerably amplified in certain circumstances Consider for example and this is based on an example found in a real life network an O D pair separated by a single link of 100 metres with signals at the downstream end such that at equilibrium the correct solution is an all or nothing flow along that link even if the signals turn out to be over capacity Since in that case more distant O D pairs would have options to divert further up downstream to avoid the congested signals but the only option for the local O D pair might
239. ns and Facilities 15 56 7 4 Motorway Weaves in Aggregated Networks The necessary flow calculations required to invoke the motorway weaving rules see 15 40 4 3 may be obtained far more efficiently using Network Aggregation if all the nodes within the motorway weaving section have been aggregated 15 56 7 5 High Priority Nodes for Aggregation 15 56 8 5120257 Apr 15 Section 15 In the cases of both banned turns and motorway weaves in order to insure that the required nodes are in fact aggregated since the final set of nodes to be aggregated is effectively arbitrary those nodes are assigned a high priority which means that in terms of steps 5 and 6 in the algorithm described in 15 56 3 they are preferentially aggregated at an early stage of the process independent of the number of arms per node Once all the priority nodes have been aggregated the process proceeds as described in 15 56 3 Further Research Despite the impressive reductions in cpu time achieved with the current techniques there are almost certainly further improvements possible Thus the rules that are used to determine when a node should be aggregated and indeed the order in which nodes are considered are highly empirical and their efficiency is highly dependent on unknown factors e g how many new links will form duplicates which may be subsequently removed A more intelligent set of rules would doubtlessly lead to further improvements in cpu t
240. ns of the simulation link record normally used to specify the number of lanes i e columns 12 to 15 see Sections 6 4 1 and 6 4 9 4 Thus 3W or W3 would both denote a 3 lane link where weaving takes place Note that the link where the W is added is the middle link in the weaving section provided that there is only one intermediate link and that nothing needs to be added on either the links which enter the weaving segment or that exit e g entry and exit ramps On the other hand if there are multiple intermediate links as in Fig 15 3 then a W must be added for all those links otherwise a non fatal error results and the weaving movement is ignored 15 40 4 2 Network Geometry 5120257 Apr 15 Section 15 In either case a number of geometrical conditions need to be satisfied Figure 15 5 A weaving section with intermediate links 1 10 11 19 20 3 Thus the on or upstream node will normally be a 3 arm priority junction with 2 one way in bound links feeding a single one way out bound link i e in bound motorway and in bound ramp feeding the out bound motorway In more precise geometric terms there must be only one permitted turn from the entry ramp link the first geometrically possible turn and only one permitted turn from the motorway the second geometrically possible turn so that both have the same exit arm Thus one cannot have an exit from the motorway onto the ramp arm entry and exit ramps must therefo
241. nt to A N plus N A since even though the movement may be valid in the original network it can never be part of a shortest path tree Note that in this case if all the original links are 2 way then the original network segment contained 6 links as does the aggregated segment So if we have not managed to reduce the number of links we have at least removed one node which given the form of equation 15 x should still lead to an overall reduction in cpu time On the other hand if one of the original links were one way imagine that A N were one way for example then the original segment has 5 one way links but the aggregated segment has only 4 A C A B B C and C B and therefore the numbers of both nodes and links has been reduced A common example of a 3 arm node might be an entry ramp onto a motorway where A N would be a one way entry onto a motorway with one way links B N and N C In this case 3 links are reduced to 2 The entry ramp configuration may be generalised to any node that has a single one way exit and n one way entries such that n 1 links are reduced to n Equally all nodes with a single entry and multiple exits may be aggregated to save one node and one link Indeed a node with any number of entry exits may always be removed by aggregating pairs of entry exits The example of a 4 arm node is illustrated below A 15 160 SATURN MANUAL V11 3 i SATURN Special Options and Facilities which reduces to D N
242. nto their own procedures Or it may also be feasible for users to set up their own equations calculations using the data manipulation facilities within SATDB 11 10 8 1 Alternatively in order to encourage the consideration of pollutant emissions SATURN contains some fairly simple minded internal procedures for the estimation and display of five standard pollutants carbon monoxide carbon dioxide hydrocarbons nitrogen oxides and lead The estimation procedures are similar to those used to estimate fuel consumption i e a linear model with explanatory variables of time distance primary and secondary stops Hence the basic equation for the emission of pollutant i from a link is E aid a t a t a 5 ais V where d is link distance tc is average cruise travel time on the link tq is the time spent idling in queues at junctions S1 is number of primary stops per vehicle S2 is number of secondary stops per vehicle V is the vehicle flow ail ai2 are user set coefficients lt needs to be emphasised that this is an extremely crude model Moreover the default coefficients given below are even worse If it gets to within an order magnitude of the true answer it will be doing well The main reason for including it at this stage is to provide for examples options in P1X to display emissions per link or options in SATLOOK to print totals Improved models with more reliably 15 85 SATURN MANUAL V1 1 3 SAT
243. ntre point in pixels and next to click on two points and input their X Y network co ordinates The four corner points may then be easily calculated via a simple linear transformation A practical problem which arises in the above procedure is that it is not possible within P1X to simultaneously display both the bitmap and the network prior to calibration We therefore recommend first viewing the bitmap e g enter it within PMAKE or use any other graphical system such as Paint in order to identify the two points nodes to be used and then viewing the network in P1X and using the X Y monitoring option under Information to determine write them down the two sets of co ordinates Armed with this information you can return to P1X and the bitmap display to complete the calibration Both procedures may be carried out at the same time by having two program windows open or even two computers This process is probably most easily done by using PMAKE to select view and calibrate the omp file and then exit the program Trying to do the same process within P1X leads to problems of having both a bitmap and an incompatible network both trying to define a network window Once calibrated a xyb file is automatically created so that picture omp spawns a file picture xyb and which will from then on be opened at the same time as the omp file is opened Outputting Bitmaps to Hard Copy Devices Bitmap files may be included in output hard copy plots
244. nvergence of the full model run not just the SAVEIT accuracy Counter intuitive results from economic evaluation techniques such as TUBA or COBA may be simply a consequence of poor convergence in either or both the do nothing and do something model runs Note that the trip matrix necessary as an input to TUBA may be dumped from MX using the standard option to dump a matrix as comma separated CSV output see 10 15 N B The problem noted above with respect to the uniqueness of the sub components of generalised cost i e time distance etc is potentially a problem for all economic evaluation procedures There is therefore a very strong case for basing economic evaluation on the generalised cost as used in the traffic assignment model which has the advantage of being uniquely determined although there are still problems of convergence accuracy as opposed to relying on sub components such as O D time and distance which are not unique Single User Class Networks The required matrices for a network with a single user class may be produced by a specific bat file sattuba bat which is run by a command such as sattuba net which takes as input a network file net ufs and outputs up to 3 matrices in text format net_d txt net t txt net m txt 15 100 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 41 3 15 41 4 15 41 4 1 5120257 Apr 15 Section 15 net_p ixt where the first matrix contains
245. o SATNET The data is then stored on the SATURN UF files and may for example be later displayed using SATDB for alpha numeric output or P1X for graphical output Knobs particularly post SATURN 10 3 have a number of possible applications Thus they may be used as components of generalised costs in particular as tolls or they may be used to define extra travel times or delays to bus services 15 44 These applications are described below Alternatively they may be used to store network data which has no direct impact on traffic assignment in which case SATURN Is being used primarily as a network data base described next Data Base Applications There are many possible applications of such a data base For example one might store the date at which a link was last re surfaced and thereby produce plots of all links re surfaced in a given year or range of years using the SELECT facility in P1X equally one might store accident statistics for links Indeed it is now quite feasible to use SATURN purely as a network data base by simply building a network in which all the standard link variables such as time etc are ignored and concentrating only on the extra data items From the network build program SATNET one could go directly to the display programs SATDB and P1X Once input certain basic algebraic manipulations may also be performed on the data using SATDB For example if you input accident statistics and calculate link flows
246. o equivalent time One solution is to set CROWCC F as recommended and post 10 9 the default in which case the distances will not be added in the original network file An alternative is to use the parameter XCCSK eXclude CC in SKims within the SATTUBA control file see 15 41 4 above to effectively set the time and distances 15 102 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 42 15 42 1 5120257 Apr 15 Section 15 for all centroid connectors equal to zero in which case they make no contribution to O D skims which are therefore based entirely on real network components only XCCSK is new in release 10 9 but is retrospective in the sense that 10 9 SATTUBA may be applied to ufs files created prior to 10 9 Note that XCCSK applies only to skims of time and distances not to skims of e g tolls or generalised costs and that it is also used more widely within time and or distance skims see e g SKIMTIME and SKIMDIST in 15 27 7 Its default F is set within the preferences file SATLOOKO DAT A further example occurs when two zones both have centroid connectors feeding in out of the same simulation node in which case the obvious path consists of an entry connector to the stop line at the node a single turn at the junction followed immediately by an exit connector In this case the O D pair will have positive time from the turn but zero total distance since both turns and simulation cen
247. ode its B node and the corresponding link number used to define that link in the output cba COBA file We propose a standard extension of cln Coba Link Number for such files such that net ufs would produce a file net cln To create a cln file use SATDB and choose starting in the Master Menu 6 Miscellaneous Data Input 12 COBA Network Link Numbers 13 Dump the Full Data Base to an ASCII File Master Menu and create the file with extension cln A batch file to do the job automatically could be created if desired requests bribes to DVV 15 106 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 42 5 15 42 6 5120257 Apr 15 Section 15 To use a file say net_base cln within another network net_ds ufs you must first create a control file coba_ctl dat which might contain amp PARAM KNOB 1 KNBFIL net_base cln amp END and then run SATCOBA via SATCOBA net_ds KR coba_ctl The output COBA file net_ds cba would then contain inter alia flows on all the links contained in net_base cln using the same link number conventions Note that links which are in net_ds but not in net_base cln would not appear in the cba file However they are listed in the output lpd file in order to help the user decide whether to include them somewhere else within the coba file Equally links which are in net base cln but not in net_ds would not appear in the output cba file Thus the only
248. of link flow Note as well that the distinction between demand and actual flows as described in Section 17 2 also applies to all the different definitions of flows along a simulation link Thus the actual upstream exit flow on a link may be less than the demand upstream exit flow due to queuing upstream Pcu s Cars Buses and Vehicles General Principles In theory the units used to describe traffic flow in SATURN can be anything the user likes e g the trio matrix can be units of cars vehicles pcu s or whatever The only real restriction is that the link saturation flows and the trip matrix elements must be defined in terms of the same units In practice however it is strongly recommended that trips and saturation flows be defined as pcu s and most printed text assumes this to be the case Strictly speaking and for pure buffer networks flows do not necessarily even need to be defined per hour they could be defined as e g daily flows as long as all appropriate commodities such as capacities are defined in the same units However moving away from hourly rates causes problems for the simulation where the length of the simulated period LTP may only be defined in minutes and the definite assumption is that the flows being simulated are hourly flows Note that the same rule also applies to all input counted flows see 6 10 and 13 1 4 i e that they should always be in the same units as all other
249. old ERL file The thought here is that if users wish to mark certain error messages as being OK e g by writing a 1 in the second field then the new ERL file simply carries this information over If no match is found the second identifier defaults to 0 Thus the intention is that users might input the ERL file output by SATNET into say Excel and then add their own numerical marks therein before either re creating a new ERL file for subsequent use by SATNET or inputting the new file directly into P1X in order to highlight certain nodes See 15 58 2 Hence the procedure could be used as part of an audit trail where errors which have been checked and approved might be assigned one numerical values and errors which have not been checked could be assigned a different value It must be emphasised that at this stage in its development the concept of a ERL file is still highly fluid and we are very much open to suggestions from users as to the basic format and contents of such files and equally the uses to which they might be put Display of ERL Data in P1X ERL data may be displayed in P1X by highlighting nodes see 11 6 5 4 based on the values in either the first or second extra identifier fields described above The options are entered via menu choices 1 or 2 ERL Field within the Display sub menu These options differ from the normal highlighting procedures which highlight nodes based on all errors detect
250. on each arm correspond exactly to 15 88 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 37 15 38 5120257 Apr 15 Section 15 those assigned This procedure would also account for any missing turn flows due to pre loaded flows Repeated Assignments Modelling Cold Starts etc The SATRAP option within the Assignment Tree Building sub menu within SATDB repeats a full assignment to the same routes and in the same proportions as in the final assignment or strictly soeaking the final assignment as re created under SAVEIT see 15 23 Thus re assigning the original trip matrix should give the same demand link flows as already stored on the ufs file So why bother Firstly SATRAP allows the user to investigate the impact of assigning a different trip matrix to the same routes One of the sub options within SATRAP allows the user to modify the matrix using random numbers in order to model the impacts of day to day variability A further option allows the user to assign trips over only a section of the O D routes defined in terms of distance For example you may ask for only the first up to 500 metres from the origin to be loaded the obvious application of which is to model vehicle flows when the engine is still cold Alternatively the flows may only be loaded beyond say 500 metres to represent warm vehicle flows Adding the two together gives total flows In the case of the critical distance falling
251. on for using the extension ufn is that this is the extension required by SATALL for an input network Provided that old_base ufs was well converged in the first place and the cost flow curves for the fixed nodes are stable then the differences between old base ufs and new_base ufs should be minimal And hopefully new_base ufs will converge much more rapidly Creating a FCF Scheme Network using SATNET Having created a master network e g new_base ufs above in which certain simulation nodes have been designated as FCF that information may be passed to a new do something network to be built by SATNET from a dat file say scheme dat by making use of the UPDATE facilities Thus if UPFIL new_base ufs UPDATE T and also a new parameter UPFCF T under amp OPTION then not only are all the normal network parameters in scheme ufn copied from new_base ufs but equally any simulation nodes which have been designated as FCF in new_base ufs will also be so designated in scheme ufn Plus the FCF flow delay parameters in new_base ufs i e to A n and C will also be passed as fixed parameters into scheme ufn The expectation is therefore that the modified scheme network with its added FCF nodes and consequently a reduced number of proper simulation nodes will converge much better and therefore any comparisons between new_base ufs and scheme ufs will have fewer problems with noise Viewing FCF Nodes within P1X Nodes w
252. or user class 3 The default is FALSE for all user classes Setting CLIMAX T i e no subscript sets CLIMAX n T for all user classes n by default unless a specific record is included for an individual user class Note that CLIMAX n is only relevant if CLICKS n has been set So unlike CLICKS there is no problem with having CLIMAX n T for all user classes since normally there should be at least one user class to which CLICKS is not applied In addition CLIMAX is a function of user class only and applies to all links or strictly speaking all links where CLICKS is less than the free flow speed Link Times Incorporating CLICKS By default the link travel times generally calculated and e g displayed by P1X do not include any extra times associated with CLICKS for particular user classes in effect they represent travel times by cars Post release 11 3 it is possible to calculate and display an average travel time representing a flow weighted travel time over all vehicle classes Thus Tet Diy Aty Vit dD Vi Where tw is the weighted travel time T is the normal time A tu is the extra travel time for user class u Vu is the flow for user class u Where flows are expressed either in units of vehicles hr or PCU hr The weighted times are calculated within SATALL once the assignment simulation loops have converged and are then stored in DA codes 4008 weighted by vehicles hr and or 4018 weighted by PCU hr They may then
253. ore fall into that category Otherwise multiple equilibria may occur In practical terms as mentioned above the use of CLICKS may influence route choice by user class The extra time penalties will automatically be included within any O D skim that includes time Summary statistics listing the total extra travel time in terms of pcu hours incurred under CLICKS are given in the lpt files and within the various list options under SATLOOK and P1X The outputs are disaggregated by user class simulation buffer this next total time period and by capacity index In principle these totals could and possibly should be added to the cruise time etc totals which appear in standard output tables however for the time being this has not 15 117 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 47 2 15 47 2 1 been done in order to allow users to think about exactly how they would wish to have the data presented In summary setting a value for CLICKS is an extremely simple method to represent differential soeeds by user class but some users might feel that the possible errors introduced at high flow levels may outweigh the advantages of simplicity Disaggregated Levels of CLICKS KLUNK Prior to the release of version 10 7 the value of CLICKS for a particular user class applied equally to all links excluding centroid connectors post 10 7 CLICKS may be disaggregated either by a link s capacity index or ultim
254. ore it is not for example possible to restrict bus lanes to certain companies or to require that only trams may use offside lanes N B The above rules were only added in release 11 1 Prior to that all bus flows were assigned to a bus lane if one were available Delays in Bus Lanes Note that a bus lane in SATURN is assumed to go from the upstream entry line to the downstream stop line set back bus lanes are therefore excluded In addition buses in bus lanes form separate queues and therefore have different 15 90 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 39 3 15 40 15 40 1 5120257 Apr 15 Section 15 delays from normal traffic making the same turning movement In effect we assume that the exclusive lane continues through the junction to the next link s entry line where it may of course meet up with a further bus lane More specifically the delay to a turn from a bus lane is equated to the minimum delay associated with normal turning traffic i e to in equation 8 5a Moreover this delay is fixed independent of the volume of traffic in the bus lane Travel time speed along the link itself equals the cruise time for normal traffic and the same link distance is assumed Clearly this model is only an approximation which will hopefully be improved with later versions of SATURN It does however include the two most salient features of such bus lanes i e that buses sho
255. ork data file with some additional parameters to control the CASSINI process A CASSINI Control ASCII file that defines the convergence strategy strategies to be implemented and An ASCII report file on the Demand Model convergence which defaults to a DIADEM output file SATURN NETWORK FILE As noted above to operate CASSINI a number of new parameters need to be added to the existing OPTION section see 6 1 in the SATURN Network data file as described below CASINI CASTXT FILCAS FILGAP If TRUE CASSINI will be called within SATNET and a number of additional checks will be undertaken to ensure the files named below exist If any of these files do not exist a semi fatal error occurs Specifies the type of demand model used and the file format and other operations that CASSINI will expect There are currently two options either DIADEM file format and CASSINI will extract the convergence of the demand model from a standard DIADEM report file a illustrated below this is the default option or A simpler OTHER file format with the file consisting of two data fields in CSV format The first value is the demand model loop number whilst the second value specifies the GAP SD convergence of the demand model The file name of the CASSINI Control file defining the convergence strategy to be applied see below for more information Default blank i e no file defined at this stage The fil
256. ormat integer values per record the first two being the link A node and B node and the third being the group The use of negative node numbers to indicate ranges is not permitted with L2G files Currently L2G files are only processed within SATLOOK i e it is not possible to define an L2G file as a namelist parameter in a network dat file and have the appropriate aggregation statistics calculated within SATALL and stored on UFS files in the same way that node based aggregate statistics may be set 15 182 SATURN MANUAL V11 3 SATURN Special Options and Facilities 15 60 5 FIL 2T Text Definitions Files with extensions of the form Z2T N2T etc etc are used to supply alpha numerical titles to Zones nodes as indicated by the first letter in the extension They are not however generally available to users at present 5120257 Apr 15 15 183 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 61 Version Control JOB NUMBER 5120257 DOCUMENT REF Section 15 doc Revision Purpose Description 10 9 10 SATURN v10 9 Release 04 09 09 10 9 12 SATURN v10 9 Release Full 31 10 09 22 06 10 06 12 10 10 9 17 Web release Jun 10 31 05 11 17 03 13 30 04 14 26 09 14 22 01 15 22 04 15 5120257 Apr 15 15 184 Section 15
257. osed although this is not a rigid requirement in SATURN that all 2 N2G G2S etc files should a have the same root filename and b be stored in the same folder In other words files such as mapping z2g mapping z2s mapping g2s etc would all be stored in the same folder and therefore have a common root pathname as well as a common filename The advantage of this is that the user need not define all the possible mapping files since a SATURN program could logically infer a file path name when necessary In particular this facility is routinely used with text descriptor files of the form G2T whereby if the predicted file mapping g2t can be found it is used to add text names to groups if not group text names are simply ignored FILZ2 Zone Aggregation Z2G All files which map zones into more aggregate structures such as groups sectors etc have the same general very simple format described as follows They consist of a series of text records terminated by a 99999 record where each record consists of two integers in free format i e including CSV specifying a zone followed by its group where we use the terms zone and group to denote the first and second quantities as in a Z2G file but the same specifications apply equally to all such files Note that numerical names must always be used for both the zone and the group not sequential numbers although very often zone and or group names are
258. ote that here if all arms are two way then we actually increase the number of links from 8 to 12 in order to remove 1 node although if one or more of the arms are one way the increase in links is reduced and may even represent a reduction E g 2 one way entry links and 2 one way exit links reduce 4 links to 2 15 56 2 3 Application to Spigot Zone Connectors A not uncommon coding trick used in SATURN is illustrated below where a zone Z rather than being connected onto a link A B directly is connected by an external simulation spigot or stub node S which is in turn connected to an artificial mid link node M See also Sections 16 6 2 to 16 6 4 and 11 9 4 1 Z However in the assignment network representation of this section of the network where mini nodes are created at the start and end points of all one way links the situation would be as follows 5120257 Apr 15 15 161 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 We therefore note that traffic leaving the network from zone Z has only two possible paths available to it Z S1 M1 M8 B2 or Z S2 M2 M4 A2 Equally there are only two possible paths into Z from A1 or A2 Thus in this situation we may aggregate the network into 4 aggregate links Z B2 Z A2 B1 Z and A1 Z while at the same time removing all the mini nodes at S and M Assuming all links are two way this remov
259. out a corresponding xyb file being located the user is offered the option to calibrate the bmp file as detailed in 15 43 3 Co ordinate Systems Once again the importance of having a common system of co ordinates for both the network and the omp files cannot be over emphasised The simplest method is to base both upon some standard system such as in the UK context the Ordinance Survey OS co ordinates with both east west X and north south Y co ordinates defined to the nearest metre Very often the leading digits as used by the full OS system may be dropped e g if all your X values begin with say 45 followed by 4 digits then it is easier to drop all the 45 s and stick to the final 4 digits Note that defining co ordinates as metres implies that XYUNIT should be set to 1 0 its default And we strongly recommend that such a system be adopted throughout This means that networks which for one reason or another have been defined from their birth using OS based co ordinates will find it much simpler to use omp files than networks which are based on a more arbitrary set of co ordinates In the latter situations it is probably far easier in the short term to convert xyb co ordinates to the arbitrary system see 15 43 3 below rather than trying to convert the original X Y co ordinates However on the other hand there are considerable longer term benefits e g being able to interface with various GlS based
260. ow speeds distances etc which may well be identical on parallel routes on later iterations where flows are essentially continuous variables equal costs are much less likely Another reason may be the treatment of possible U turns at simulation buffer boundaries In any event the final differences should be relatively small and it should be borne in mind that both solutions are equally valid Alternative Tree Building Algorithms Having established a different form of network on which to build trees it should equally be feasible to create different tree building algorithms that take advantage of the new network properties 15 56 5 1 Duplicate Links 5120257 Apr 15 Section 15 For example aggregate networks tend to have a large number of duplicate links i e joining the same two nodes together whereas these are not permitted in normal networks The reason that they are not permitted in normal networks is 15 165 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities not because they are judged not to exist but due to the technical problems of being able to uniquely identify links by their A node and B node e g in a counts file The reason that duplicates can arise in aggregate networks is illustrated below with a segment of a grid network lf node D is aggregated a diagonal link from C to B will be created whose cost is equal to the costs of CD plus DB Similarly if A is aggregated anoth
261. owever still function with e g elastic assignment or multiple user classes Think Link Weaving and W Turn Priority Markers There are certain obvious parallels between the phenomenon of weaving on a link as described above and of weaving at a node as described in 6 4 2 5 and based 15 98 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 40 8 15 41 15 41 1 5120257 Apr 15 Section 15 on the use of W turn priority markers In both cases 4 sets of individual flows come together and depending on the level of crossing over reductions in Capacity and increased delays may result The precise mechanisms by which these effects are modelled within SATURN are different however Thus W priority markers are modelled essentially as a form of give ways at a single junction controlled by parameters such as GAP whereas the link weaves use quite formulae and quite different parameters and apply over more than one coded node Link weaving may be seen as weaving over a distance whereas W priority markers represent weaving at a point effectively therefore over much shorter distances The choice of one form over the other should therefore be partly governed by the distance over which weaving is felt to take place Display of Link Weaving Data E g P1X Each link which has been coded with a W is assigned a numerical marker which indicates inter alia its position in the sequence Thus
262. ows 1 SATBUF old_base to create old_base buf with all simulation links in old_base ufs converted to buffer format 2 SATCCS old_base to create old_base map with all simulation centroid connectors converted to buffer format 3 SATCH old_base control where control dat includes INCLUD T in order to produce INCLUDE files control_11111 dat control _22222 dat and or control _44444 dat to represent simulation data within the central cordoned area At this stage we now have all the necessary components to create a new network data file new_base dat as follows 4 COPY old_base dat new_base dat 5 Edit new_base dat using a standard text editor e g NOTEPAD in which we a Delete the existing 11111 22222 and 44444 if it exists data segments and b replace them by INCLUDE references to control_11111 dat control 22222 dat and control 44444 dat c Add 2 extra records INCLUDE old_base buf and INCLUDE old_base map within the 33333 data segment but do not delete any of the existing 33333 data records Thus at the end of the edit we have a network dat file in which the 11111 22222 and 44444 data segments refer specifically to the central cordoned network while the 33333 data segment has had extra data added in the appropriate format to represent the former simulation links and centroid connectors in the intermediate band We note that the two 33333 INCLUDE segments added in step c above will a
263. parameters used listed below and the best fit value of N are for a nominal dual 3 lane motorway with 15 HGVs Figure 15 3 re plots the same data as delays versus flows which is the form in which it is applied in assignment models Further advice is provided to assist in converting curves into a form suitable for SATURN in the following section The equivalent SATURN parameters for the curves illustrated above with various assumptions on the other COBA parameters required are shown below S Description 111 8 1046 reas 410 6990 20 Note speeds So S and S in km h whilst breakpoint F and capacity flow C are in pcus h 15 23 COAT ON ere Vp44ec SATURN MANUAL v11 3 ananial A TH SATURN opeclal U gt Figure 15 2 COBA11 Piece Wise v SATURN Power Based Speed Flow Curve 15 HGV 120 10 SATURN Power Curve 100 D COBA Piece Wise 90 80 70 60 50 Speed km h 40 30 20 10 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Flow pcus h 15 HGV HGV 2 3 pcus Figure 15 3 SATURN Dual 3 Lane Motorway Flow Delay Curve SATURN Power Curve COBA Piece Wise Travel Time for along a 10km link seconds 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Flow pcus h HGV15 HGV 2 3 pcus 15 9 4 Conversion of existing speed flow curves into SATURN Extreme care should be exercised when
264. ph 2 26 in DMRB Volume 6 Section 2 Part 1 TD 22 92 gives a formula for the number of traffic lanes required for weaving Equation 15 3 N Elon tOu 2 0 240 1 act Where N Number of traffic lanes required Gw Total non weaving flow in vph Quwi Major weaving flow in vph Qwe Minor weaving flow in vph D Maximum mainline flow in vph per lane refered to as S below L min Desirable minimum weaving length Lani Actual weaving length available in metres referred to simply as L from now on 15 92 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 where Lacq is assumed to be greater than Lmin and if not take Lmin Lace Such that the factor within the bracket multiplying Qwe 3 In SATURN we need to invert this equation since the actual number of lanes provided Na is already specified by the SATURN input along with its natural saturation flow which determines capacity and what we need to know is how much the saturation flow capacity is reduced by the effect of weaving Thus we begin by factoring all the flows Q in Equation 15 2 by a uniform factor F such that the required number of lanes given by Equation 15 2 equals the number of actual lanes N i e F Q are the flows at capacity Equation 15 4 F Q O X Q N S Where F required factor S the saturation flow per lane as input by the user and ignoring any effect of wea
265. r a new ufs file and optionally a new dat file must be explicitly set within control dat but that a file net rgs is always output with its filename fixed by the input network net ufs PARAMETER TYPE DEFAULT FUNCTION NAME SIGOPT LOGICAL TRUE If TRUE optimise green times SATOFF LOGICAL FALSE lf TRUE an offset optimisation is carried out prior to green time optimisation SELECT LOGICAL FALSE lf TRUE read a set of selected nodes to be optimised from this file immediately after amp END see also 11 9 13 2 RESIM LOGICAL FALSE lf TRUE a complete simulation is carried out prior to the output of ufs file MYTVV INTEGER 1 Stage time Optimisation algorithm See 15 31 3 NOPMAX INTEGER 1 Maximum number of internal iterations used by the signal setting routines see 15 31 3 MANOFF INTEGER 0 The signalised simulation node number used as the reference point for all optimum offset set by SATOFF See 12 2 3 FILDAT CHARACTER Blank Defines an output dat file FILUFS CHARACTER Blank Defines an output UFS file RECORD S 2 Selected Signalised Nodes One node number per record in free format terminated by 99999 to select a subset of nodes to be optimised for both stage times and or offsets Using SIGOPT for Base Year Networks In principle there should be no need to run signal optimisation for base year networks where the stage times should be directly obtainable from observation and one would hope SIGOPT would give
266. r the supply demand cobweb loops Typically a relaxed set of convergence criteria would be set for the initial loops when supply demand convergence is poor and the trip matrices are still highly uncertain but these would be subsequently tightened as the overall model convergence improves in other words reducing the over convergence within the supply model i e SATURN See section 7 4 5 3 for a more general discussion of the principles applied by CASSINI Appendix R contains a copy of the ETC2009 paper that describes the practical benefits of CASSINI within a full WebTAG compliant demand model Basic Principles Given a fixed trip matrix SATURN uses internal loops between its assignment and simulation sub models as well as internal iterations within the two sub models in order to achieve an overall equilibrium solution in terms of path flow choices as best represented by its gap value see 9 2 1 15 148 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 A characteristic of the process is a rapid initial descent before a much more gradual approach to a highly converged solution as shown in Figure 15 11 below In this example to achieve a GAP value of 0 05 requires around 20 times the CPU time to achieve a GAP of 5 0 eight times the time to achieve a GAP of 1 0 and four times the time to achieve a GAP of 0 5 respectively Clearly significant CPU savings may b
267. r the convergence of linked supply and demand models 7 8 6 or for economic evaluation models where the demand evaluation model is based on a different definition of generalised cost from the assignment model and therefore requires separate skims of time distance etc The problem is most acute if a high degree of convergence is required It may also have implications for economic evaluation models when applied to relatively small schemes when any source of noise in time and distance etc matrices is a problem The problems of non uniqueness may be further aggravated by the presence of residual path flows in the solution used which may make skimmed quantities considerably more unreliable than say flows See 15 57 The problems of non uniqueness for time and or distance skims may be particularly evident when comparing skims from two different schemes where for example there may be large differences in individual O D times or distances when none might be otherwise expected These differences may be due to network 1 using an arbitrarily different set of OD routes from network 2 and if there is a large degree of variability between the times distances on the alternative routes even though they may have identical generalised costs then there will equally be a high degree of variability in the time distance skims 10 The degree of variability may also depend on the relative cost weights i e 11 PPM and PPK ass
268. re be defined at distinct nodes Equally the off or downstream node will also be a 3 arm priority junction with one one way in bound arm feeding two outbound one way arms The entry motorway arm must have both its two possible turns defined the first to the off ramp the second continuing along the motorway and the off ramp link must be one way out bound In practice both the on and off nodes will be 3 arm priority nodes as described above However strictly soeaking the nodes may have more than 3 arms as long as the extra arms and turns do not interfere with the required geometry For 15 96 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities example the nodes could include both the entry and exit ramps on either side of a motorway with the two motorway arms being two way but the turns on one side of the motorway could not cross those on the other side In general such coding is not recommended particularly if weaving is being modelled each direction of the motorway should contain distinct nodes and links lf there are one or more intermediate nodes such as nodes 11 and 19 in Figure 15 5 then each should be essentially a two arm priority with a single one way exit feeding a single one way exit Such nodes might be added in order to provide shape to the network although it should be noted the shape may also be obtained via a GIS file see 5 7 15 40 4 3 Assignment Calculations 15 40 4 4
269. re to choose the best order and to avoid double counting etc Pre Load Statistics The assignment network statistics include totals for any pre loaded trips separately from the over all totals but as of yet no comparable breakdown is available within the simulation network Pre Loading from a Text Data File lt is also possible to input pre loaded flows from a text based data file as opposed to a SATURN ufs file post version 10 4 For example if you have extensive bus flows but do not wish to code them as individual routes only to represent their total flow across the network then it may be done by setting up a text file wherein 15 11 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 9 5 5120257 Apr 15 Section 15 each record contains a link identification in standard or free CSV format see below followed by b the corresponding flow in units of pcu hr Alternatively if the pre load file and the current file have a different network structure and pre loading from a ufs file is not permitted paragraph 4 15 5 1 then the relevant flows may be pre loaded by first dumping flows from the pre load file into a text file e g use SATDB 11 0 9 SATURN differentiates between the two by looking it the extension of the input file if it is ufs ufa etc it assumes a SATURN file if not it assumes a text data file See 14 4 4 The format of the link identification may either follow standard S
270. reased to 10 There may therefore be a strong case for using NUCUJT to selectively set relatively low values of NUC for say roundabouts and priority junctions NUCJT 1 NUCJT 3 5 where resolution is not an issue but larger values for signals NUCJT 3 25 such that the overall soace requirements are not increased Equally increased NUC values also increases the CPU time required to carry out a simulation although generally this does not lead to significant increases in overall run times since particularly in large networks it is the assignment that takes up almost all the CPU time 15 38 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 15 3 5120257 Apr 15 Section 15 We may further note see also the final paragraph in 15 15 3 that having different values of NUC at two adjacent junctions has no real effect on the transfer of cyclic flow profiles between them since CFP profiles will be suitably transformed Final thought Low NUC values do not necessarily lead to errors in the simulation what they do do though is to introduce a certain level of clunkiness into the simulation which may be counter productive in terms of convergence Increasing NUC values in an existing validated network is unlikely to change it into a non validated network but it may improve convergence and it may produce noticeable changes at a small number of turns LCY Cycle time The choice of LCY can however
271. referred to as DfT but for historical reasons also referred to as DTp 15 9 2 DFT DTp Advice Note 1A DTp Advice Note 1A recommended curves have the following form t V d S V Sy V lt F S V 4S S S V F C F F lt V lt C S 1 S V C 8dC V gt C t is the link time in hours d is the link distance in kilometres S is the link speed in kph V is the link flow in PCU per hour So is the free flow speed S is the speed at capacity F is the maximum flow at which free flow conditions hold C is the capacity We wish to fit the above curve in the range V lt C with a function t t aV The three unknowns to a and n are fitted from the following constraints 1 Free flow times must be the same hence ty d So 5120257 Apr 15 15 19 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 2 Capacity times must be identical and 3 The average travel times must be the same Condition 3 is the critical one for determining n We define the average travel time to be C t v avic 0 Hence for SATURN the average time is given by t t aC n 1 C t aC n 1 t t C t n41 Integration of the DTp curve gives t t 1 F C In S S 1 t 1 t t Hence n r 1 I F C rnr r 1 1 1 where r S S t t A section of FORTRAN code which does the above job is given below R S0 S1 XN 0 0 IF R GT 1 0 THEN XBOT 1 0 F C
272. rements If a larger version is required please contact Atkins to discuss your specific requirements Pre 11 2 several variants of Level N3 were created to accommodate the suite of sub regional models developed by Transport for London with various bespoke configurations to accommodate their specific requirements With the release of 11 2 the internal array dimensions were restructured to provide a new Level N4 to meet all their anticipated requirements but within a much smaller RAM footprint Therefore there may be some issues of backward compatibility for very large networks using SPIDER Network Aggregation and the standard N3 will not necessarily be capable of running the TfL Sub Regional HAMs and an upgrade to Level N4 will be required The values of the above dimensions for a particular set of executables may be established via Help About in the P1X menu bar or the full set is contained in the on output files from SATNET Note that one particular array dimension that controlling the maximum size of a trip matrix within SATALL may be effectively increased in size by the judicious use of a parameter SPARSE see 7 11 12 Further details on the financial implications of upgrading your existing version are may be found on the website www saturnsoftware co uk 15 29 Comment Cards and Blank Records in Data Files In theory any ASCII file used as input to a SATURN program e g the dat file input to SATNET may contain co
273. restimate that particular turning movement The capacity is that already calculated for each simulation link see 8 9 4 for further details while the flow delay power n is a weighted sum of individual turns as with delays above Both the order and the format of the output variables is the correct order required by buffer network input to SATNET section 6 5 Thus the times capacity and distance are all output as integers although they are calculated as reals 15 17 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 8 3 15 9 15 9 1 5120257 Apr 15 Section 15 Note that SATBUF deals only with simulation links i e the 11111 data input and that users must decide for themselves how to deal with simulation centroid connectors the 22222 data inputs One very simple solution which implies using an editor is to edit the 22222 records by inserting a C in every column 1 deleting all records from column 11 onwards This has the effect of producing a correctly formatted set of buffer link records with the zone as A node and the first simulation node entered as its B node Whether this is a good way to re code centroid connectors is another question N B If DUTCH T in the network being bufferised then an alternative version of the batch file may be run thus SATBUF net DUTCH in which case the new link A nodes and B nodes will appear in column blocks of 10 not 5 in the output fil
274. rices may be constructed Thus if the cost per link is a weighted combination of say time and distance such that Ca W t Wed Then if we take forest skimmed matrices of time and distance t and dj then we can also obtain the average cost matrix C via Ci Wi ti Wo dij This method is sometimes necessary if for example the user wishes to define different values of the weights w and wz se 7 8 6 15 67 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 27 5 5120257 Apr 15 Section 15 Skim Cost Matrices and Trip Matrices It needs to be appreciated that skimmed and or cost matrices in general are calculated entirely independently of any considerations of demand and actual flows on individual links Thus the O D distance in a distance matrix is the sum of the individual link distances along a particular path or paths whether or not the O D trips use those links in the current or a later time period Demand and actual flows play no role This may have certain implications for matrix based evaluation procedures and in particular for the interpretation of the product of a trip matrix and a skimmed matrix i e under what conditions will the following equation hold DTS LVS ij a where the left hand side of the equation represents the total say vehicle kms summed over ij pairs and the right hand side represents the same quantity summed over links and displayed in o
275. rithm proceeds as normal with the one exception that step 3 see section 7 1 2 build minimum cost trees and load all O D trips to the minimum cost paths uses the aggregated network This is turn involves two extra steps 1 Prior to tree building calculate the current cost of each aggregated link by summing the costs of its constituent links and 2 Post loading transfer the flows onto the aggregate links back onto their constituent normal links to obtain Fa n All other FW steps e g the optimum combination of link flows and the calculations of the objective function in step 4 are all based on the basic network definitions Note that steps 1 and 2 above are repeated once per user class for MUC assignment While steps 1 and 2 are an extra overhead on the normal all or nothing loading sequence which increases cpu these are compensated by the reductions in cpu time for tree building and loading per origin and provided that the number of origin zones is large the latter will always outweigh the former Indeed the larger the number of zones the more cpu time will be saved lt should also be noted that the aggregate version of Frank Wolfe may occasionally give different results to the normal version One reason arises when there are two equal minimum cost routes between two nodes and the one selected is essentially arbitrary Equal cost routes occur most commonly on the very first iteration where the costs are based on free fl
276. rk following the same basic procedures as for standard networks but with one preliminary step calculate the time or whatever quantity is to be skimmed per aggregate link CPU savings accrue from being able to reconstruct the minimum cost paths per iteration using the much more compact aggregate network such that similar time savings to those illustrated above for assignment should also be achieved for skimming See Section 15 27 7 2 for information on aggregate skims within SATLOOK as selected by a parameter USESPI Aggregated networks are also optionally used for Select Link Analysis within P1X see 11 8 1 12 also controlled by a parameter USESPI Tracing Paths in Hybrid Networks For certain applications it is possible to trace paths through a hybrid network which consist of a mixture of both aggregate and normal links Hybrid networks were first introduced in release 11 2 3 in February 2013 For example if in the above example of the basic path A B C X Y Z one were doing a select link analysis of link K L one could analyse a path that used the aggregate links A G M R and R Z but for the section G M which contains the individual link of interest K L one could revert to a basic network trace G H l J K L M Thus the hybrid network is formed of aggregate links where no events of interest e g a selected link occur plus normal network links in the vicinity of events In so far as the majority of links
277. rtaken using SATALL involves an iterative looping process between successive assignment for tree building and loading and simulation for junction interactions However only the main assignment routines are undertaken in parallel and therefore the benefits of SATALL Multi core are dependent on the time taken within the assignment and simulation routines Similar results were found in other models but the performance gains will be dependent on a large number of variables including the PC hardware available and the SATURN model used SATALL Multi Core is also compatible with Network Aggregation techniques see Section 15 56 and the performance gains are independent and hence typically multiplicative Further information may be found in Appendix S 15 53 3 2 SATLOOK Skims Multi threaded 5120257 Apr 15 Section 15 At present multi threaded versions of SATLOOK may only be run within a limited number of applications batch files which skim costs specifically SKIMTIME SKIMDIST SKIMPEN SKIMTOLL SKIM_ALL see 15 27 7 and SATTUBA see 15 41 1 The performance gains for such routines are similar to those produced by SATALL with reductions of up to 3 5 times on a Quad core PC see Figure 15 9 for applications of SKIM_ALL Performance benefits continued to improve with five cores but there was some erosion of the gains beyond six cores 15 145 SATURN MANUAL V1 1 3 Special Options and Facilities SATURN Figure 15 9 SATL
278. s well as the normal assignments to reduce CPU but there are also certain Improvements that are only feasible within SAVEIT In particular the trick to eliminate zero flow links within a SPIDER assignment see 15 56 5 3 may be used to great effect within a SAVEIT assignment In addition post release 11 2 a SAVEIT assignment may use an Incremental Assignment 7 11 12 to initialise Frank Wolfe Assignment with the objective of reducing the onset of residual paths To invoke incremental assignment set the parameter INKS_S in the network dat file to say 4 to request 4 increments Empirical tests to determine whether or not the method is effective are under way so it should be considered as an experimental option While in principle the SAVEIT assignment should converge to an identical solution to the full assignment in practice due to lack of convergence etc it is 15 51 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities psy toe ag 5120257 Apr 15 Section 15 only an approximation and the flows and assigned routes etc differ Although the higher the level of assignment convergence the better the approximation will be See 15 23 4 for a discussion as to how the parameters NITA_S and UNCRTS may be set to ensure optimum convergence The differences between true and SAVEIT assignments can have important implications for e g skimmed matrices as used for economic evaluation or variable demand
279. s a string of zeros Their intentional use is not recommended at all in particular since there are exceptions to the above rule For example numerical KNOB data contained on extra lines in network dat files may legitimately contain all zero entries and be correctly represented by a blank line 15 14 5 Equally key files and GRAF DAT may contain all blank records There may be other examples but we havent thought of them yet Prior to 10 5 blank lines were not explicitly detected and could give rise to fatal errors e g if they were meant to contain node numbers The Use of Sub Files within Data Files INCLUDE Certain data sections within e g network dat files allow sub files to be referenced by inserting a record containing the characters INCLUDE starting in column 1 followed by a file name which should be read at that point For example the sequence 66666 Sue TUDE Eeer enolic 99999 in a network dat file requests the program to read the bus route data from a file metro bus Note that the filename need not be enclosed in inverted commas i e metro bus not metro bus unlike filenames etc which are specified within Namelist inputs see Appendix A However if they are the s are removed and a warning printed in the LP file Note that the file metro bus should not contain the opening 66666 record but should contain a closing 99999 record which indicates only that reading rever
280. s are the greater the savings in CPU time N B Both UPDATE and PASSQ 17 3 1 allow the pre network to have a different structure from the main network whereas at the time of writing the pre load option PLOD does not see 15 5 1 This is likely to change in the future Note that the UPDATE option as described here implies that only the network is updated although it is also permissible to introduce a different trip matrix at the same time If however one only wishes to change the trip matrix then the appropriate steps are described under the Re start Facility in Section 15 4 In order to ensure that the first assignment within the assignment simulation loop takes full advantage of the improved initial set of flow delay curves the maximum number of assignment iterations normally set by the parameter NITA is set to the maximum of NITA NITA_S and 25 It is possible post SATURN 10 6 for a file to in effect update itself in the sense that an old UFS file say net ufs may update a new network data file net dat In other words it is not necessary to re name the network every time a minor change is made and the results from the previous incarnation are used to the full Note as well that if UPDATE is set to TRUE but the UFS file to be updated has not been defined then it is assumed by default that the file to be updated IS net ufs when the data file is net dat This option is particularly useful whe
281. s have been created within SATURN in order to simplify and automate the creation of minimum and or averaged cost etc matrices Thus the bat file SATCOST automatically extracts the minimum as opposed to average cost matrix as defined in 15 27 1 and is available both within DOS and SATWIN For example the command SATCOST net cij Generates the matrix of minimum o d costs for network net ufs and stores them in cij ufm Type SATCOST for full filename conventions This is usefully coupled with elastic assignment to generate cost matrices for external demand models see 7 8 6 If the input network contains multiple user classes the calculations include all user classes and the output matrix is a stacked matrix one level per user class Similarly if the input network has an extension uft i e it represents the outputs of multiple time periods then the output matrix cij ufm will be stacked by blocks with each block see 10 2 4 representing the o d costs for a particular time period Note that SATCOST and all the variants below produce cost matrices defined in units of generalised seconds which are therefore compatible with the units used within all elastic or variable demand models Equally note that the units are effectively O D travel cost per pcu and bear no relationship to the trip matrix or any factors used e g to factor trip matrices For example if you have a model with a single total trip
282. s may simply be due to some minor artefact of the algorithm used From which it follows and this is the important point that any outputs from a route flow analysis such as a Select Link Analysis or skimming say distance from a forest 15 27 6 are also non unique and therefore prone to being arbitrary A knock on impact of skimmed times distances etc etc being non unique is that any further analyses based on those skimmed matrices becomes non unique This therefore may introduce further problems with economic evaluation packages such as TUBA or external demand models VDM which are not based on generalised cost matrices generated by SATURN which are unique see also 7 8 6 Secondly there are potential problems with the all or nothing division of O D routes into used and non used Thus a rat run route which includes a large proportion of very low capacity links may be allocated O D route flows if it is a minimum cost route whereas an alternative route along a series of high capacity motorway links may not be used at all if its generalised cost is just 1 second above the minimum Small changes in either the network or trip matrix may reverse either allocation On a more positive note one could argue that given its sequence of operations the Frank Wolfe algorithm is unlikely to produce a totally unbalanced or extreme set of O D route flows Equally it treats all origins equally and simultaneously and will
283. s not recommended The choice of optimisation algorithm 1 to 5 above is set by the parameter MYTVV as set in amp PARAM either in the SATNET dat file or in the control file to SATALL lt needs to be emphasised that this procedure is largely experimental and we have very little experience so far to compare the results from the above procedure from that using the explicit SATED SATALL loop Since the updates are more frequent in SATALL one per loop one might expect to find better signal settings and lower travel times using this method but life is not necessarily Straight forward with network models However using SIGOPT T within SATALL is likely to lead to over estimates of network performance as noted in 15 31 1 and it should therefore be used with some caution and only if the resulting signal times and flows are carefully analysed for realism The same note of caution should also be applied to the use of SATOFF T within SATALL In particular since the optimum offsets are most sensitive to link cruise times which are generally fixed as opposed to turning delays which may vary 15 81 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 31 4 1 15 31 5 15 31 6 5120257 Apr 15 Section 15 considerably with iterations of SATALL the optimum offsets per node may only change once within SATALL and the same result could be obtained by using the program SATOFF on its own Using SATOFF T on its ow
284. saggregate statistics are calculated within SATALL When this happens a warning message is generated lf BYGRUP F then the disaggregation is potentially set by the link capacity indices but only if a a further namelist parameter BYCAPI T and b capacity indices exist in the network Since as explained above capacity indices may not be all that useful for disaggregate statistics BYCAPI defaults to F The disaggregate statistics calculated by SATALL and stored within the UFS file may be viewed only within SATLOOK option 4 then 1 from the main menu see Section 11 11 4 Disaggregation within SATLOOK As mentioned above disaggregate network statistics as optionally calculated within SATALL may only be accessed using SATLOOK either the standalone version or called from P1X However it is also possible to calculate similar Statistics on the fly within SATLOOK using not only those criteria available within SATALL e g disaggregation into traffic boroughs but also by a much wider range of possible disaggregation rules main menu option 4 followed by option 2 Thus the most basic level of link disaggregation is set by the parameters BYGRUP TFL and BYCAPI if any of these three is toggled interactively then the link sub sets will be re calculated and the disaggregate statistics will be re calculated and output In addition the N2G file which would have been initially set as a network dat file parameter may be re d
285. scale interurban networks for which junction modelling is not essential Another example would be the user who wishes to use the matrix update facilities within SATURN without necessarily wishing to define all or part of his network in the detail required by SATURN A third example is the use of SATURN purely as a network data base The ASCII dat file necessary to define such a network must commence with the three mandatory input records OPTION namelist title and PARAM namelist as described in Section 6 immediately followed by a buffer network header record of a3 in column 1 and the buffer network description terminated by a 99999 card as specified in Section 6 6 Node co ordinates route flows etc optionally follow The final card in the file must be another 99999 card The use of default speed flow curves within the 333 records 15 9 5 may be extremely useful in buffer only networks Thus a typical file might read amp OPTION amp END THIS IS A PURE BUFFER NETWORK amp PARAM BCRP 4 0 LIST T amp END 33333 3 56 2500 29 42 1250 2 56 3750 2 3 C C 99999 55555 Co ordinate data 99999 99999 End of file 15 16 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 8 2 5120257 Apr 15 Section 15 Converting Simulation Networks to Buffer SATBUF For various applications it is sometimes useful to convert a network with a simulation component either entirely or in
286. signment is based on pure time In this situation the skim matrix Sj is effectively the same whether it is obtained as a minimum cost matrix or as a forest skim to the extent that under perfect Wardrop Equilibrium all used paths have equal and minimum cost Clearly if the convergence is not perfect then the equality will be only an approximation 15 68 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 27 6 Summary Minimum and or Skim Matrices 5120257 Apr 15 Section 15 This section summarises several common sources of confusion experienced by users faced with the problem of producing cost and or skimmed matrices in general 1 A matrix of say O D distances times tolls etc may be produced in at least three different ways where we assume first that the assignment is not based on minimum distance a building minimum distance trees b skimming distance along the single path minimum cost trees c skimming average distance along the forest of multiple paths used within the assignment These correspond to minimum cost matrices Option 14 in SATLOOK skimmed matrices Option 14 in SATLOOK and forest skims Option 9 in SATLOOK and or batch files such as SKIMDIST 15 27 7 respectively It is important that users understand how these three types of matrices differ Of the above three methods the third i e the forest skim 15 27 3 Is almost certainly the most realistic since it
287. since none of the steps described above introduce new nodes plus a set of new aggregate links joining those nodes Note that the number of zones remains unchanged and therefore the proportion of zones within nodes as well as the proportion of centroid connector links within links increases significantly In addition an aggregate network may contain a significant number of duplicate links i e links with the same A node and B node the reason for which is discussed below Both of these slightly unusual network properties may lead to variations in basic tree build algorithms becoming effective see below Note that the sub set of nodes which are retained within the aggregate network may be selected and therefore highlighted within P1X see 11 6 3 5 Implementation within SATNET A semi empirical methodology has been introduced into the network building procedures within SATNET to produce an aggregated network activated if a amp PARAM parameter SPIDER is set to TRUE default FALSE It proceeds via a number of successive steps as follows 15 163 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 1 Aggregate certain priority nodes i e buffer nodes where there are banned penalised turns and weaving sections where aggregation is essential for the modelling see 15 56 7 3 2 Aggregate all spigot centroid connectors 15 56 2 3 Aggregate stub link c
288. sing with six or more cores The performances gains are clearly dependent on the SATURN model and computer hardware used 15 53 3 6 Running More than One Multi Core Assignment In Section 15 52 we describe how SATURN may be used and controlled to undertake parallel operations The same procedures may be used with SATURN Multi Core without any change to those procedures 15 53 3 7 SATCH_MC Distributed Trip Matrix Cordoning A distributed procedure SATCH_MC may be used to create a multiple user class cordoned trip matrix by creating cordoned matrices by user class within separate processors and then finally creating a full stacked trip matrix by stacking the individual sub matrices using MX See 12 1 6 15 53 4 Multi Core Parameters 15 53 4 1 Options To activate the multi threaded operations within SATALL and SATLOOK once installed the amp PARAM namelist parameter MULTIC is set to TRUE in the network dat file and the Windows Operating System handles the allocation of the computational calculations between the available threads available The value of 5120257 Apr 15 15 147 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities MULTIC parameter is stored in the network binary files ufn s and the value read by SATALL SATLOOK etc where necessary An additional integer namelist parameter MCALG selects one of a set of optional algorithms which are basically provided for internal testing We recommend
289. single user class we continue to store cost and there is no reduction in size Note that the default value of UFC111 is T meaning that post 11 2 the option to output times rather than costs is virtually always invoked for MUC UFC files and indeed UFC111 should only be set to F for test purposes NITA_S and UNCRTS Accuracy of SAVEIT UFC Assignments The final SAVEIT assignment which creates the ufc file and the corresponding route flows may use a different maximum number of Frank Wolfe iterations via the parameter NITA_S Thus if NITA_S is non zero it replaces the value of NITA see 7 1 5 in the final assignment This option is useful if you have been using a relatively low value of NITA within the assignment simulation loops not a bad idea with DIDDLE see 9 5 2 but you want a more representative single final assignment Increasing NITA_S leads to improved convergence of the SAVEIT assignment and therefore should reduce but not eliminate the problems of approximation referred to above 15 23 2 Thus the default value of NITA_S is 99 whereas the default value of NITA is only 20 Users frequently increase NITA_S to even larger values e g 256 For similar reasons the value of UNCRTS which also controls the number of iterations undertaken by a Frank Wolfe assignment see 7 1 5 may also need to be reduced in order to prevent the SAVEIT assignment terminating prematurely Post release 11 it is set equal to the best GAP value 9 9 1 2 ach
290. speed flow curves which have been developed in a different context are translated into SATURN speed flow curves We note in particular problems which have arisen in using COBA 10 curves 5120257 Apr 15 15 24 Section 15 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 9 5 5120257 Apr 15 Section 15 whose basic application is within an economic evaluation package not within an assignment model Certain of these problems apply more to the use of link capacity restraint curves within the simulation network 6 4 12 and 8 4 4 most apply to both simulation and buffer networks equally The first concerns the question as to whether or not the recommended capacity for a link A B takes into account the existence of a intermediate junctions between A and B or b the junction at B In a buffer network both a and b should be included in the capacity used by SATURN in a simulation network a should be included but not b which is otherwise considered by the simulation of junction B The problem is therefore one of either double counting or zero counting See also 6 4 12 1 The second problem is one of units If as in COBA 10 capacities are normally specified in units of vehicles per hour there may be an assumed percentage of HGV or other vehicles within the vehicles Thus given a link with a flow of 1 000 vehicles hr of which 15 are HGVs 150 hr for which one would
291. t and signal optimisation using a number of different signal control policies as given in section 15 31 38 Interested readers are referred to the classic tome on the subject Route Choice and Signal Control Avebury Press by Tom van Vuren and Dirck Van Vliet Under certain circumstances this approach can lead to considerable reductions in total travel time eg up to 20 compared to the initial and therefore potentially arbitrary settings in the base network However a closer examination of the process shows that this is often obtained via a process in which flows and green times move in small steps in consistent directions with the process only terminating once the stage times reach their minimum values Such solutions are also characterised by near all or nothing flow patterns whereby very high flow rates with corresponding near maximum green rates occur on certain well defined corridors whereas parallel routes are virtually unused These solutions argue a a large degree of co operation between drivers and signal setters and b that drivers can detect and react correctly to very small shifts in green times It is therefore our belief that such solutions are not entirely realistic and may actually over estimate the level of performance of a network Therefore the use of an optimal iterative strategy must be viewed with extreme caution See also 15 31 4 15 78 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15
292. t distinguishes between separate turning movements at nodes but with fixed and therefore separable cost flow or flow delay curves FCF for each turning movement which should improve convergence and reduce noise FCF may be thought of as another form of perturbation assignment see 22 2 6 or diagonalisation see 9 1 2 The essential idea is that in the intermediate FCF network the flow delay curves for the simulation turns are fixed after a certain number of simulation assignment loops see Fig 9 1 presumably once a reasonably good level of convergence has been reached Thus given the general flow delay equation of the form see Section 8 4 2 Equation 8 1 reproduced t AV t V lt C a t AC t B V C C VC b The parameters t A n and C are all treated as fixed for individual turns rather than as variables calculated at the end of each new simulation A further property of an FCF Fixed Cost Flow description is that the same network properties may be applied to both a do minimum and a do something network in order to minimise noise between the two Finally we note that the structure of the assignment network in which simulation turns are represented by individual links is also unchanged under FCF it is only the nature of the cost flow curves on these turn links which has changed This in turn implies that a basic Frank Wolfe assignment step will r
293. t of DIADEM this increases the number of matrices which may be stacked and unstacked but the number is still potentially limited See 14 8 UFMSTACK AND UFMUNSTACK These new bat files allow matrices to be stacked and or unstacked with effectively no limit on the number of levels user classes which may be accommodated See 10 20 17 and 10 20 18 SAVEIT Unless you specifically need to create skimmed matrices of time distance etc in order to run the demand model within DIADEM which in general terms we do not recommend see 7 4 5 3 and 7 8 6 or you are using a warm start we recommend that you set SAVEIT F and avoid the excess CPU of creating UFC files which will not be used at the end of each run of SATALL Note that if required a UFC file can be created at the very end by running the procedure SATUFC see 15 23 5 N B This does not apply under OBA where the overheads associated with SAVEIT T are minimal SKIM_ ALL If however the Diadem model requires skimmed matrices of time distance and or tolls on each supply demand loop it will save CPU time to use the simultaneous skimming procedures embedded in SKIM_ALL see 15 27 7 rather than skimming each component separately Further general advice on linking SATURN with external variable demand models such as Diadem as given in Section 7 4 5 Users may also wish to note that the Gap convergence measure used within Diadem has an equivalent measure within SATEASY
294. t zero opposing flows down to zero at Vm Sy or strictly speaking CAPMIN see 8 2 3 with a power defined by G Syj In general TRRL models predict a linear relationship between C and Vy so that in order to reproduce this same form in SATURN it is necessary to set G 1 Vy i e set the gap parameter GAP to the inverse of the saturation flow of the controlling arm s Very often the GAP values derived in this way seem small particularly when interpreted strictly as a gap in traffic that entry traffic would accept For example if the controlling saturation flow were 3 600 pcu hr then GAP should be one second It must however be appreciated that GAP is essentially a parameter fed into a model Such models are only approximations to reality and contain a number of intrinsic errors specification errors which to a certain extent can be corrected or counter balanced by changes to the model parameters For example the gap acceptance model in SATURN assumes random Poisson cross traffic ignoring for the moment cyclical effects whereas in reality one knows that traffic tends to come in surges the effect of this being that the random model tends to under estimate capacity Empirically if we accept the TRRL relationships as correct then the best value to choose for GAP is 1 Sy We may also note that the standard default value of GAP set by SATURN is 5 0 seconds which is almost certainly on the high side causing the SATURN simu
295. tance time and or charge matrices all need to be path weighted averages i e the travel time averaged over the paths used by each O D pair as opposed to being say the time component along a single minimum generalised cost path or even the time along the minimum time path In SATURN terminology TUBA requires skimmed matrices as opposed to cost matrices see Section 15 27 4 Hence SATTUBA requires that the network is set up with SAVEIT T and the skims are based on forests not trees We note that as explained in 15 23 2 and 15 27 5 the forest path flows generated by SAVEIT are not necessarily exactly equal to the path flows generated during the true assignment Thus quantities such as total pcu hours pcu kms etc calculated using the skimmed and demand trip matrices which is effectively what TUBA seeks to do are only approximations See 15 23 2 for a discussion of how these approximations may be improved We further note that quite apart from numerical uncertainties arising from the method of calculation and or convergence there are further theoretical problems in that in principle Wardrop Equilibrium does not yield unique values of O D time distance or toll On the other hand it does yield unique values of OD generalised cost See below and sections 7 1 6 7 8 6 and 15 23 8 for further discussion In a wider context it also has to be remembered that the accuracy of a skimmed matrix is also affected by the overall co
296. ted into an extended UFO OBA format Thus path based assignment see 21 4 stores the exact path data in UFQ files while OBA stores the equivalent splitting factors in UFO files see 22 5 2 In both cases the information saved is exact unlike the link based UFC files which see 15 23 2 above may be an approximation based on an extra SAVEIT assignment We note that path based UFQ files are restricted to single user class assignments only so that in terms of practical applications they are not really relevant and they are not considered further In principle the same forms of analyses such as those listed in 15 23 1 may be carried out under all 3 methods although the precise algorithms used to do so may differ Thus UFC based algorithms based on a Frank Wolfe assignment recreate each individual O D path used in the assignment in order to analyse them as appropriate path based algorithms analyse explicitly saved paths in the same way while UFO based algorithms use splitting factors in a single pass per origin without explicitly re creating O D paths see 22 5 2 Note that in practice some of the necessary programming work may not have been done yet for certain combinations of method and analysis UFO vrs UFC lf say both UFO and UFC files are available for a particular network the user may have the choice as to which to use for example carrying out a Select Link Analysis in P1X 15 19 PIJA calcul
297. ternatively SATTUBAO outputs its matrices as SATURN ufm files whereas SATTUBAS outputs them in TUBA Format 3 Otherwise the formats filenames etc are the same as under SATTUBA The number of decimal places used in text output formats e g CSV files may be user set via a parameter NDPS in the standard SATLOOK preferences file satlook0O dat or via user set file see 15 41 4 The current default is 4 Note that there is no SATTUBA2 procedure since TUBA Format 2 does not make much sense in this context Equally there is no SATTUBA 1 since that is what SATTUBA does O D Speeds in TUBA XCCSK We note that TUBA uses the O D time and distance matrices produced by SATTUBA to construct its own internal matrices of average O D speed which in turn it uses to estimate fuel consumption and vehicle operating costs Problems may arise if either the time or distance matrices contain artificial elements or have certain components missing leading to unrealistic speeds Thus if buffer centroid connectors have been created with either a distance and no time or a time and no distance then the summed O D times and or distances may lead to very high or very low speeds The most frequent inadvertent cause of this is when SHANDY T and CROWCC T see 15 10 3 in which case a buffer centroid connector which is defined in the network dat file with both time and distance fields blank will have its distance set equal to the crow fly distance but n
298. the default value of 1 A further integer PARAM Namelist parameter MICNUM defines the maximum number of core processors to be used on the computer default O meaning use all available threads See 15 53 4 2 below For the other Multi Core programs i e SATPIJA SATCH and SATUFO the Multi Core batch files have to be used 15 53 4 2 Upper Limit on MCNUM Values 15 94 15 54 1 15 54 2 5120257 Apr 15 Section 15 The SATURN MC will require more memory than the standard versions dependent on the number of threads available Within the software there is no restriction set on the maximum number of threads that may be used For the distributed processes a practical limit of 8 eight was coded but for version 11 3 onwards the limit was increased to 32 SATURN CASSINI Overview CASSINI is a Visual Basic program developed to significantly reduce SATURN runtimes when SATURN is used within a Variable Demand Model such as a simple DIADEM model or a more complex bespoke modelling system See Section 7 4 1 for a general discussion of the problems of convergence between supply i e assignment SATURN and trip matrix demand models and Section 7 4 5 for a description of the iterative cobweb loops between supply and demand models whose runtimes CASSINI seeks to optimise CASSINI enables the user to automatically adjust the convergence targets set for each run of SATURN to match the current level of convergence achieved fo
299. ther inputs in control dat including the definition of the cut links etc etc which define the innermost network retain the same formats With DOFCF T an additional output binary network file old_base ufa is created with the arbitrary file extension UFA which retains the same network topology as old_base ufs but with three components simulation FCF and buffer as opposed to the two original components simulation and buffer in old_base ufs See 12 1 11 Thus the cordoned network which is normally created as a separate self contained network by SATCH defines the innermost pure simulation component of old _base ufa the remainder of the former simulation network becomes FCF 15 3 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 1 5 15 1 6 15 1 7 5120257 Apr 15 Section 15 and the buffer component if any is identical between old_base ufs and old_base ufa Note that neither an output network data file control kp which normally defines the cordoned network nor a cordoned trip matrix are required in this operation the sole purpose of running SATCH in this fashion is to produce the new three level network UFA file Therefore to save unnecessary calculations and CPU the parameter DOMAT should always be set to FALSE To complete the first stage the file old_base ufa should be renamed copied as say new_base ufn and run through SATALL in order to create new_base ufs The reas
300. though it is recommended that a maximum of 4 be used so as to keep the formats neat Equally zone numbers are still effectively limited to a maximum of 5 digits see 5 1 6 More specifically formats in the following programs are altered as indicated below A SATNET SEE SECTION 6 A 1 THE BUFFER NETWORK DATA CARDS SEE 6 6 Col 1 A C if the following node refers to a zone Cols 2 10 The A node for the link Col 11 A C to indicate a zone number following Cols 12 20 The B node for the link Cols 21 25 The link time in seconds or speed in kph at free flow conditions Cols 26 30 The link time in seconds or speed in kph at capacity Cols 31 35 The one way link capacity in pcus per hour Col 38 A one way two way indicator Col 39 An S if soeeds were defined above otherwise times are assumed Cols 41 45 The link distance in metres Cols 46 50 The power to be used in the link flow delay curve Cols 53 55 A link index in the range 0 999 Cols 56 80 Optionally up to KNOBS extra data items A 2 The Restricted Turns or Links See 6 7 Cols 11 20 The B node B Cols 21 30 The C node C blank or 0 in the case of a link Cols 31 35 The ban penalty indicator for user class 1 Cols 36 40 Ditto for user class 2 Cols 41 45 etc 15 45 SATURN MANUAL V1 1 3 Special Options and Facilities SATURN Cols 11 20 The B node B A3 NODE AND
301. thought of as weighted differences of the link flows weighted by time distance or cost If the two assignments are self consistent all the above statistics will equal zero larger values imply that the various options listed in 15 23 1 will only generate approximate answers and the statistics give a quantitative estimate of that approximation The difference statistics are also held in the output ufs files and may be examined using the analysis option 8 within SATLOOK and or under Analysis etc in P1X 11 8 4 7 15 52 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 23 3 UFC109 UFC111 Alternative UFC files In order to remove some of the uncertainties associated with SAVEIT assignments an option has been introduced in release 10 9 to create UFC files which reproduce exactly the iterative costs used by Frank Wolfe and in a more space efficient format It requires that a logical parameter UFC109 is set to TRUE under namelist PARAM in network dat files Thus if UFC109 T default T two things happen 1 The costs stored are those from the actual assignment see 15 23 3 1 2 Times not costs are stored under MUC see 15 23 3 2 In addition post release 11 2 the second option is independently controlled by an alternative parameter UFC111 such that if UFC111 T then times are always output not costs independent of the value of UFC109 15 23 3 1 UFC109 T Storing True Frank
302. tic than those calculated at the end of the assignment and therefore the best estimate of O D costs would be obtained using these costs Again the same caveat as above applies to the routes actually calculated using these costs i e they do not necessarily correspond to routes generated by the assignment although they are unlikely to be unrepresentative routes Times 1 8 and 4 can be selected by the user via menus in SATDB SATLOOK and P1X Times 2 are effectively only available through the options to loop over each iterative set of costs to construct each built tree in turn Extended Travel Times The basic link travel times for cars as defined in 15 24 2 may need to be extended to include additional time components as required in certain circumstances The need arises very often when different user classes have different speeds and in particular when time is being skimmed see 15 27 7 1 as opposed to being used to set minimum cost routes Thus by default link time penalties as defined under the network 44444 data records 6 8 are by default included within the normal definitions of skimmed time on the basis that they are more likely to be real times rather than notional times added by the user to improve the assignment routings Note that the 15 61 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 24 5 15 25 5120257 Apr 15 Section 15 contributio
303. tion network as described in Section 15 8 Preliminary tests may now be carried out with very little coding effort 15 18 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities Certain problems may arise in converting existing speed flow curves into the flow delay relationship as specified by SATURN for its buffer network i e an nth order power law for flows less than capacity and a linear relationship for flows above Capacity see Section 5 4 and equation 5 1 These problems may concern not only the calculation of n dealt with below but also problems with the interpretation of parameters such as capacity We consider first the range of flows less than capacity V lt C Clearly if the existing curves are already in the form of a power law then the problems here are minimal the user must simply ensure that the required value of n is set in BCRP if it is constant for all links or is input for each individual link If however the existing curves are of a different form it will be necessary to define power law curves which in some sense give a best fit to the existing curves There are many ways in which this can be done depending both on the definition of best fit as well as on the shape of the existing curves Different countries may well have different recommended forms We illustrate here one method which may be used to convert curves of the form recommended by the UK Department of Transport currently
304. to TRUE on amp OPTION in the new network DAT file Input the UFS file from the previous sequence on channel 2 to SATNET which may most easily be done using the parameter UPFILE see section 6 1 to define the filename We note that this procedure is very similar to the PASSQ option 17 3 1 which also if UPDATE F extracts flow delay data from a previous network file in this case the PASSQ file from the previous time period The difference under UPDATE T is that only flow delay information is extracted from the update file not the queues and suppressed traffic as with PASSQ 15 7 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities Note that both UPDATE and PASSQ may be used at the same time but if so they must use two different input ufs files parametric filenames UPFILE FILUP and FILPQ respectively If only PASSQ is used then there is no option to cancel the flow delay updates The extended SATURN procedures may be used here the command format is illustrated in Section 14 4 2 Further Notes 1 5120257 Apr 15 Section 15 The second network may in fact be structurally quite different from the first in the sense that new nodes and new links or turns can be introduced The program is set up in such a way that only information on turns and links common to both networks are carried over For new turns default flow delay parameters are assumed Clearly though the more similar the two network
305. to the next assignment from the pure simulation network since the cost flow curves are identical they only diverge thereafter to the extent that the simulated cost flow curves change By contrast SBT networks give quite different results immediately since the buffer link representation is based on a quite different and arguably less realistic network representation than the simulated turns Therefore in terms of realism FCF is preferable to SBT On the other hand in terms of CPU and convergence SBT is the winner in that the reduced network size roughly speaking including turns doubles or more the size of the assignment network leads to faster run times plus arguably faster convergence Note that the original trip matrix is still valid for the transformed networks whether under FCF or SBT since the zone structure has not been changed at all in the new networks Preferences files All interactive programs require a preferences or initialisation control file in order to set default values for various parameters The files are assigned standard names such as P1X0 DAT MX0O DAT etc i e program name 0 dat They consist of a set of namelist based definitions of purely internal program variables which control for example the size of arrows in node graphics These therefore are the variables whose values are changed by users via the standard menus Formal definitions of the valid variable names in each file
306. troid connectors have zero distance by definition In this case there are fewer simple remedies within SATURN N B SATTUBA ts still very much work in progress and not all the final essential options have been added We therefore welcome feedback from users SATCOBA SATCOBA is a procedure embedded within SATDB which enables a sub network of links to be defined which is compatible with that required by the economic assessment program COBA and in addition to output a text file which specifies the network and includes flow data and selected link data as required by COBA in the formats required by COBA Alternatively a sub set of links as would be used by COBA see paragraph 1 in 15 42 1 may be selected within SATDB after which the user is free to output whatever data they wish in whichever format they wish as opposed to SATCOBA which outputs fixed data in fixed formats General Functionality COBA requires that the network be defined in such a way that a there are no centroid connectors only real links and b all links are bi directional i e if a link A B is included it represents both the link from A to B and that from B to A or in the case of a one way link only the direction that exists Thus the first job carried out by SATCOBA is to define an appropriate sub network Note that within this sub network node names are those used by SATURN but each link is given a unique number which equals its normal link
307. ts to the original file at that point Strictly soeaking the 99999 record is optional as an end of file has the same effect however the use of 99999 records is strongly recommended if only to positively affirm that this is the end of the desired data The original file must therefore also contain a 99999 record in the normal way to indicate the end of a data section 15 76 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 The facility is available within SATNET to read any of sections 1 through 8 in the network input data files It is being gradually extended to other programs and or files e g counts in SATPIJA see 13 2 1 and may also be used within Namelist inputs see Appendix A It may also post 10 9 be subscripted so as to apply to a particular time period under multiple time period modelling PASSQ see 17 4 4 in SATNET For example SINC UDE Ii owe IL seletc SUNCIVUIDIE 2 lowe 2 cleue in a network dat file would indicate that two different sets of bus routes were to be included in the first and second time periods See Appendix B An example of a network dat file which makes extensive use of sub files is given below SINCLUDE 444 DAT 99999 55555 SINCLUDE XY DAT 99999 66666 SINCLUDE BUS DAT 99999 77777 SINCLUDE COUNTS DAT 99999 77777 45 53 32 33 COMMENT 33 34 7 8 99999 77777 SINCLUDE COUNTS3 DAT 99999 There are many possible
308. uivalent information for methods 2 and 3 is given briefly in 15 23 6 and in more detail in Sections 21 4 and 22 5 2 Under method 1 for every assignment iteration within the Frank Wolfe algorithm the complete set of link costs used to construct minimum cost routes is preserved in a separate UFC binary file These costs may be used later in order to re construct the specific trees from each iteration and thereby re construct the specific O D routes from that iteration for further analysis The filename convention is that if the main network file produced by SATALL is net ufs then the cost file will be net ufc In addition the ufc files record the weights as used by each iteration in the final solution see 7 1 2 15 50 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 23 2 5120257 Apr 15 Section 15 Not creating a ufc file will not affect the normal analysis or use of the ufs file except clearly if ufc does not exist then none of the above mentioned analyses may be invoked Note that ufc files etc are only used under the standard Frank Wolfe link based algorithms MET 0 see Section 21 Under method 3 the route information is stored within a UFO binary file see 15 23 6 SAVEIT UFC as an Approximation The SAVEIT Assignment Under certain fairly restricted conditions the routes and costs stored in ufc files under SAVEIT will be identical to those used to
309. ular criterion for further scrutiny How this is done within SATURN is described in Section 15 23 Select link analysis is a very powerful tool not only for the analysis of schemes but also for the validation of a base year network In many respects it is the converse of building trees in order to check on an assignment trees tell you which links are used by specified O D pairs select link analysis tells you which O D pairs use selected links Within SATURN it is possible to perform select link analysis within several different programs and with slightly different outputs although very often the same information may be obtained from two or more programs We therefore first identify the options available 15 43 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 5120257 Apr 15 Section 15 1 SATPIJA may be used to undertake a PIJA analysis whereby the fraction of trips P for each l J movement assigned to link A is stored during an assignment The main purpose of this option is to provide the PIJA or UFP file required by SATME2 and no print facilities are provided within this program More than one link or turn can be analysed within a single run 2 Program SATU2 13 7 can read a PIJA UFP file and output a matrix of trips as a UFM file using selected links MX may then be used to print the trips with the option of aggregating zone to zone trips into sector to sector trips and printing
310. uld incur lower queues and delays than other traffic and perhaps more importantly that buses in an exclusive lane do not reduce the capacity of other traffic on the same link Exits Entries from Bus Lanes At the start of a bus lane the bus traffic effectively leaves at the upstream end so that a its flow is an integral part of the previous turn unless of course this is the start of the route and b its flow is not included as part of the normal flow on the link At the termination of a bus lane the buses rejoin normal traffic upstream on the following link so that a it is not part of the final turn flow but b is part of the next link flow In some respects bus lanes may be thought of as tunnels in that as far as the rest of the traffic on the network are concerned buses disappear at the upstream start of a sequence of bus lane links and only reappear at the upstream end of the first non bus lane link Information on flows to on and from bus lanes may be obtained via SATDB 11 10 6 with up to 15 levels of flow definition available In addition a table in the pon file output by SATNET lists similar information on all links with bus lanes Motorway Weaving Segments Introduction Weaving segments on motorways correspond to the situation depicted in the diagram below Figure 15 4 whereby an entrance ramp onto a motorway is followed by an exit ramp downstream such that traffic entering the motorway and staying o
311. uld indicate an acceptable fit to a traffic modeller whether it was a difference of 325 to 4 000 or 120 in 500 while links with GEH parameters greater than 10 would probably require closer attention lt needs to be noted that the GEH statistic is an intuitive and empirical engineering measure not necessarily a measure that a professional statistician would recognise or deign to use However it should also be noted that the square of the GEH parameter is not unlike the well used chi square measure of fit and would be the same if either V1 or V2 whichever was the observed flow were used in the denominator One reason for taking the average is to avoid possible problems when either V1 or V2 equals zero It is however not particularly useful to take the comparison too far particularly when comparing modelled to observed flows since the sum of the GEH values interpreted as a chi square statistic will almost certainly indicate that the two are significantly indeed very highly significantly different and that therefore the model is wrong From a pure statistical point of view virtually all transport models are wrong in that they fail to reproduce observations What a transport modeller wants is a model which although not strictly correct is adequate for the uses to which it is applied A further distinction between GEH and chi square is that the latter gives a relatively greater weight to larger differences betwe
312. ultiple time periods and in addition to extend header records e g 100104 adds extra data to 104 so that old SATURN UF files have the same array lengths as the latest one to ensure upwards compatibility DA Codes for Actual User Class Flows Whereas there are two explicit DA codes used for total demand and total actual flows 4503 and 4513 flows by user class are only stored by demand Thus see above the demand flows for user class 1 are stored in DA code 3803 for user class 2 in 3813 etc etc and there no arrays DA codes within ufs files which directly store actual flows by user class However it is possible in certain circumstances to use DA codes 3808 3818 etc to obtain actual flows by user class 1 2 etc For example SATDB will accept such codes as a link data input definition 11 10 2 and they may also be used with DBDUMP 15 46 What actually happens however if 3808 is requested is that the actual array read in is 3803 user class 1 demand flows but the data is immediately factored down by the global ratio of actual to demand flows Thus the end effect is the same as though 3808 was explicitly stored in the ufs file DA codes 3808 3818 etc etc may also be used in P1X to create and annotate data using a DA code but individual user class flows both demand and actual may also be accessed using items in the Flow list Note that within this list user classes 1 2 and 3 are always explicitly listed along
313. units of say pence rather than seconds This is particularly useful for skimming trees as explained in Section 15 27 Note however that SATURN virtually always defines generalised cost internally in units of seconds e g when carrying out elastic or variable demand calculations Users are therefore strongly recommended to stick with generalised time unless e g they specifically require costs in some other units to be exported to some other evaluation package Stochastic Trees Stochastic trees refers to minimum cost routes between origin and destination zones hence trees built on the basis of using random number distributions to generate individual link costs hence stochastic It is therefore the process at the heart of stochastic assignment as described in Section 7 2 All programs that allow the user to build trees SATLOOK P1X and SATDB also enable stochastic trees to be built by setting the parameter SUZIE to TRUE Parameters SUET KORN and KOB then control the generation of randomised link costs in the same way as they do within stochastic assignment see Sections 7 2 3 and 7 2 4 There are two very general circumstances in which stochastic trees are built 1 To precisely reproduce the routes generated during the stochastic assignment itself and 15 62 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 26 5120257 Apr 15 Section 15 2 To generate a series of typical
314. ure The same problem also occurs in present day networks when network changes are tested The two main parameters of concern here are stage green times and offsets Cycle times generally have a smaller influence and anyway can be set as a universal parameter LCY inter green times are generally fixed by reasons of safety etc The question of setting optimum offsets is discussed in Section 12 2 with respect to SATOFF However the problem of determining optimum stage green times is considerably more complex than that of optimising offsets due to the potentially highly sensitive feedback between stage times which affect capacities and flows Basically if one sets optimum green times for a pattern of flow which is in Wardrop Equilibrium given the old green times those flows will no longer be in equilibrium since those routes which have been allocated more green times will have become faster We must therefore reassign in order to take account of the latest green times However this will tend to put more flow down those links that were given extra green time and therefore if we re optimise the green time in accordance with the new flows the more heavily loaded links will tend to be assigned more green time And more green time tends to mean more flow a vicious circle is thereby established Considerable research work has gone into the investigation of the Iterative Optimal Approach whereby a loop is established between Wardrop assignmen
315. user class 2 vehicles e g lorries have a maximum speed of 100 kph on all roads both buffer and simulation Input values of CLICKS are included as subscripted variables within amp PARAM in the network dat file the default of 0 0 signifies that there is no maximum speed restriction for that user class Units are in kph CLICKS only has an impact on road links i e buffer and or simulation roads not simulation turns and not centroid connectors whose free flow speed is in excess of the input value s of CLICKS In modelling terms it is represented by a fixed time penalty per user class equal to the difference in time between a vehicle travelling at the input free flow speed and at CLICKS if the free flow speed is less than or equal to CLICKS then the time penalty is zero And equally if CLICKS is not set the time penalty is zero But see 15 47 3 for an alternative model with variable time penalties Generally speaking CLICKS is applied to links which have a speed flow curve but they may equally well be applied to links which have a flat soeed flow curve If the link does have a speed flow curve then it would be expected that CLICKS would be somewhere in between the maximum free flow speed and the minimum speed at capacity if not a Serious Warning 159 is generated In general we would expect that CLICKS 1 0 on the assumption that user class 1 represents cars and that cars can always travel at the maximum speed i e the 15 116
316. utput tables such as Table 17 3 as described in Section 17 9 Firstly such an equality never holds if the flows Va correspond to actual link flows and the summation corresponds to say total pcu kms within this time period see Table 17 3 In particular there is no such thing as an actual trip matrix for use on the left hand side only a demand matrix Secondly if the matrix Sj has been skimmed from a single path tree then the equality will not hold in general unless most unlikely all O D trips have been assigned to single not multiple paths The equality may hold if a Tj is a demand matrix b Sj has been skimmed from a forest and c the link summation includes both this and the following time periods the Totals column in Table 17 3 However even these conditions may not be sufficient to guarantee exact equality For example if the link flows Va are obtained from the true model run and the skimmed matrix is based on a forest obtained using an approximate SAVEIT assignment 15 23 2 then the equality will only be approximate limited by the lack of perfect convergence within both the true and the SAVEIT assignment More specifically if S represents time then the parameter AFTERS must equal 0 5 see 17 6 2 Conditions becoming slightly easier if the quantity S refers to the generalised cost used by the assignment as opposed to a particular component such as time or distance or if say the as
317. ver gt Total Travel Times Total peu hrs lt Proportion carried over gt Travel Distance Tota pcu kms lt Proportion carried over gt Average Speed Overall kmh lt Ratio gt saigialalalaia g a sjelaieysiylslsas oO oO Delay Total peu hrs Delay Vehicle mins veh Congestion Index mins veh km Average Trip Length km Simulation Queues pcu h Ave Queue DA1433 Queue at End DA1463 Turn Penalties pcu hrs hy not found not found not found not found Turn Penalties number not found not found not found not found _ _ D oO r pon m No No _ No 5120257 Apr 15 15 130 Section 15 SATURN MANUAL V11 3 SATURN Special Options and Facilities 15 49 2 6 Comparing Different Networks We may also compare the summary statistics for each of the different networks eg the Development Scenario EPSOM98RXX against the Reference Case EPSOM98AXX by specifying the appropriate column ID ie C in this case EJ Microsoft Excel Summary Report v3 00 xIs aay File Edit Tools View Inserk Format Data Window Help C A Wright Atkins am 3048181 SATURN Support 2 lJWright Atkins Date Created 15 03 07 Version 3 00 Convergence Summary for EPSOMSO AAS 12 94 5 0 302 vF lows 96 S4P Statistics Summary Results FRPS
318. ving replacing D in Equation 15 2 Xi the extra weight associated with the minor weaving flow 2Lmin Lact 1 Furthermore at capacity the total unweighted flow should also equal the actual number of lanes times the effective saturation flow Se Equation 15 5 F Q a Q T Q NS Let Q QO Q X Q2 Hence from Equation 15 3 Equation 15 6 P N Q Subtracting Equation 15 4 from Equation 15 3 gives Equation 15 7 O F X 1 N S S whence Equation 15 8 S S O F X 1 N a and substituting F from Equation 15 5 into Equation 15 7 gives 15 93 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 40 3 5120257 Apr 15 Section 15 Equation 15 9 Q Hence the saturation flow is reduced by a factor W Equation 15 10 X 1 W sip Q X 1 w which may be more simply and intuitively written as w 2 Q where Q Qw Qw Qua Note that in the worst possible case when X takes its maximum value of 3 0 and Qw 0 Qwi Qw then the reduction factor W 0 5 which might be thought a bit extreme Various alternative formulations have been proposed as discussed next Extensions and Alternatives to the Basic Theory A further feature of the above model not mentioned above is that the reduction factor is assumed not to apply for weaving lengths in excess of some value Lmax typically 3 km This will introduce a discontinuity into the multiplier of Qw2 X i
319. wish to attribute a PCU factor of 2 0 PCUs HGV the equivalent flow in terms of PCUs hr would be 1 150 The third question is what happens to speeds in excess of capacity COBA curves for example may assume that speeds above capacity do not reduce but continue to be fixed at their capacity speed SATURN assumes that flows in excess of capacity lead to linearly increasing queues with a consequent linear increase in travel time reduction in effective speed as given in equation 5 1b Users need to bear this in mind in specifying link capacities for both simulation and buffer links In all three cases it is the responsibility of the user to decide how and by how much to compensate for these effects before using these curves within SATURN Default Speed Flow Curves It is possible to define the speed flow relationships on buffer links by defining default speed flow curve parameters which apply to all buffer links which have the same capacity index To use this option within a network data file input to SATNET you must Define a set of default speed flow records within the 33333 data records identified by a D in column 1 and with entries for free flow speed speed at Capacity capacity the power n and a non zero capacity index in the normal fixed columns see 6 6 for the detailed format For each buffer link to which the above parameters apply leave blank or code as zero the free flow speed time
320. with if there are more than 3 user classes a single designated user class for which the demand actual flow may be obtained By changing the definition of the designated user class within an Options sub menu flows for any user class may be obtained rather than having to use say code 3858 to get UC 6 flows Choice of Gap Parameters The choice of the parameters GAP GAPR and GAPM can have a very strong influence on the capacities and delays given by the SATURN simulation model and some care should be exercised in their choice In particular the user may wish to set parameters such that the SATURN output is similar to that given by other models in particular models for isolated junctions such as the TRRL programs ARCADY PICADY and OSCADY By a judicious choice of parameters this can be achieved The role of the gap parameters in setting the capacity of a give way movement is explained in Section 8 2 2 In the simplest possible case of a minor arm opposed by one major arm e g at a T junction or any arm at a roundabout the capacity Cm of the minor arm is given by the equation 15 48 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 23 15 23 1 5120257 Apr 15 Section 15 Equation 15 2 C 8 1 V Sy where Sm is the saturation flow of the minor arm Vy and Sy are the flow and saturation flow of the major arm and G is the gap value Hence C goes from a maximum Sm equal to its saturation flow a
321. ws that may be ignored Within SATURN we use two criteria i The absolute difference AD in costs between the cost on a path Cp and its minimum cost cj and ii The relative difference RD Cpi cj Cy AD and RD are then compared to use defined parameters within amp PARAM RESIDD and RESIDR such that if a path or a portion of a path satisfies the condition that AD gt RESIDD and RD gt RESIDR then the path is considered to be a residual flow path The default values of both RESIDR and RESIDD are both 0 0 signifying that residual paths are to be ignored Recommended values might otherwise be RESIDR 1 5 and RESIDD 60 0 in units of seconds N B These two options are only available on Beta release and will almost certainly be replaced by the use of methods to prevent residual paths occurring in the first place Avoiding Residual Flows during Frank Wolfe Assignment An alternative approach to dealing with residual flows AFTER they have been generated by an assignment is to prevent the assignment from generating them in the first place The basic idea is on very early iterations of Frank Wolfe to use an estimate of what the final converged link costs are likely to be e g from a warm start network to build a minimum cost tree per origin based on the final costs Then when building the proper FW minimum cost trees links using the current FW costs exclude any links which according to the final cost tree are
322. xample due to the origin having no out bound centroid connectors the skimmed cell in the matrix takes on a default value of zero by default Logically it might be argued that if it is impossible to get from o to d the default value should be a very large value On the other hand if the trip matrix contains a positive value in that cell for whatever reason multiplying the trip matrix by the skimmed matrix would yield very large numbers for the unconnected cells which may swamp the correct cells as part of an economic evaluation of total vehicle costs The default value may however be changed by the user within the SATLOOK interactive menus or via a parameter DEFODC in SATLOOKO dat Skimming Forests As noted above 15 27 2 skimming the single minimum cost tree to produce say distance may be unreliable and or misleading An alternative procedure option 9 within SATLOOK is to skim a forest See 15 26 whereby the distance say Is calculated using the exact routes used on iterations 1 2 3 etc and a correct weighted average distance obtained The one basic option within a forest skim is to nominate the quantity to be skimmed Generally but not always the quantity skimmed will be a sub component of the generalised cost used to define the forest e g time distance toll etc Alternative options exist to either construct the skimmed quantity from elements in the base network file select a link property wh
323. xed penalty may be seen using the above 1 km long motorway link by assuming that the speed at capacity for that link has been coded as 40 kph Under capacity conditions it is perhaps more realistic to assume that both cars and lorries travel at the same bumper to bumper speed In fact the extra 6 second penalty on the lorries will bring their effective speed down to 37 5 kph an error of 2 5 koh On the other hand it might be argued that even under bumper to bumper conditions cars will still have a slight advantage over lorries by being able to weave in and out a bit more and that maybe a differential soeed of 2 5 kph is not too bad an estimate of that effect It is up to user to judge whether or not this represents an acceptable model At this point users may well be asking why there cannot be two or more different speed flow curves per link per user class which may differ at free flow but come together at capacity In principle there is no reason why such differential curves could not be defined Unfortunately for complicated theoretical reasons the multiple user class assignment algorithm used within SATURN see 7 3 requires that there can be only one cost component which is flow sensitive and that that component i e time is common across all user classes Fixed cost components may however differ between user classes e g the evaluation of distance in generalized cost seconds and the differential time penalties must theref
324. y different set of flows although arguably they may be nearer to a true Wardrop Equilibrium solution which causes more confusion than benefit Finally note that UFO files may equally be converted into equivalent or virtually equivalent UFC files using SATUFC see 15 23 5 above and that an alternative form of UFO file may be created based on aggregated spider networks see 22 5 3 which is generally speaking much faster to use for analysis Creating UFO files SAVUFO Batch File Procedures SATUFO In order to create both a UFO and UFC output file from a Frank Wolfe MET 0 run of SATALL it is normally necessary to have both SAVEIT T and SAVUFO T within the original network dat file By contrast OBA always produces a UFO file as long as SAVEIT T The approximate algorithms used to create UFO files from Frank Wolfe assignment are described in Section 22 5 3 However alternatively UFO files may be created after the fact if SAVUFO is not T in the initial assignment by either 1 Running the procedure SATUFC 15 23 5 with an extra text argument UFO included in the command line or 2 Running a procedure SATUFO net to create a file net UFO on the presumption that the file net ufc has already been created Note that SATUFC and SATUFO are both batch files which call SATALL EXE with particular command line parameters in order to carry out particular functions i e they are not distinct exe
325. you could then calculate and analyse accidents per vehicle It is hoped that this facility will encourage other types of SATURN users apart from traffic engineers For example it might allow identical networks to be used for traffic analysis and the analysis of accidents rather as often seems to be the case with Local Authorities for two different groups to set up different networks for the same area Using Knobs within Generalised Costs Section 7 11 2 and equation 7 43 describe how the generalised cost of travel as used for traffic assignment may be defined as a linear combination of time distance and one or more knob data sets The relative weights are set by PPM PPK and knob specific weights specified within the 88888 record set 6 11 As noted in 7 11 2 SATURN makes no further assumption as to what these extra costs are really representing They might for example represent nominal time penalties in units of seconds associated with following a non signposted route However the nominal charges will not be included in network statistics of total pcu hrs 15 33 SATURN MANUAL V1 1 3 SATURN Special Options and Facilities 15 14 4 15 14 5 5120257 Apr 15 Section 15 Note that it is possible to have negative values for Knobs data which contribute to generalised cost but only if the total link fixed cost does not go negative See 7 11 2 Negative Knobs values should be used with caution although they may sometimes be use

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