Home

86-R8 - Virginia Department of Transportation

1. City amp State Traffic Prom Total Stopped Time 4 x 7 Mui Were is Stopped Delay 8 x 0 92 424 Approach Delay 3 x 1 3 4 l wo 8 Total Volume iii 220 Stopped Delay Per Vehicle 9 11 LR ed us Approach Delay Per Vehicle 10 11 4 197 D B 15 Corr Corr No 1 No N APPENDIX C CALCULATIONS FOR NETWORK COORDINATION Source Reference 12 C 1 CALCULATIONS FOR NETWORK COORDINATION 1 When two streets having signal systems intersect we have a signal network This may be an open network or a closed network LL AE OPEN NETWORK CLOSED NETWORK 2 In a closed network the timing in each direction on each street must be studied to maintain some progression in each direction if possible 3 Time space diagrams should be developed for each street separately in order to determine desirable offsets at each intersection along a street 4 Since it is difficult to show time space diagrams for a network of signal systems it is possible to use line drawings of the street network with notations at each intersection of the length of green plus yellow for each through movement and the time offset in relation to a time reference point For e
2. EVALUATION OF SIGNAL TIMING AND COORDINATION PROCEDURES Volume I Technical Report by E D Arnold Jr Research Scientist The opinions findings and conclusions expressed in this report are those of the author and not necessarily those of the sponsoring agencies Virginia Highway amp Transportation Research Counci A Cooperative Organization Sponsored Jointly by the Virginia Department of Highways amp Transportation and the University of Virginia In Cooperation with the U S Department of Transportation Federal Highway Administration Charlottesville Virginia September 1985 VHTRC 86 R8 TRAFFIC RESEARCH ADVISORY COMMITTEE L THOMAS JR Chairman State Highway Traffic Safety Engineer VDH amp T B DIAMOND District Traffic Engineer VDH amp T C HARRIS TSM amp Programs Engineer FHWA O LEIGH Maintenance Engineer VDH amp T NEAL JR Chemistry Laboratory Supervisor VDH amp T C NELSON JR Assistant Traffic amp Safety Engineer VDH amp T E PATTERSON Senior Traffic Engineer Department of Public Works Norfolk Virginia L PERRY Assistant Transportation Planning Engineer VDH amp T D SHEPARD Research Scientist VH amp TRC C TAYLOR II District Traffic Engineer VDH amp T ii TABLE OF CONTENTS 5 E REESE INTRODUCTION ae an PURPOSE AND SCOPE ans ae nee FORMAT AND USE REPORT ere ER EO FE EMT E INVENT
3. the first two cases above this time occurs while the paralle vehicular traffic or traffic on the street not being crossed is receiving a green and clearance interval Therefore the sum of the green and clearance interval for an approach should be long enough to accommodate any pedestrian flow on the cross street In many cases the combination of pedestrian and vehicular volumes may not create enough conflicts to warrant concern about the minimum time 61 needed by pedestrians At locations where there are significant pedes trian volumes or pedestrians require special attention such as near elderly housing it is necessary to provide pedestrian actuation and set the pedestrian intervals to ensure that the minimum crossing time is received Upon receipt of a pedestrian call the walk and pedestrian clearance intervals for the phase controlling traffic on the street not being crossed will begin timing and extend the green to the set values if necessarv In other words if necessary the minimum green is reestablished based on a pedestrian demand This separate timing may or may not be in conjunction with separate pedestrian sianals The walk interval or time needed by a pedestrian to perceive the signal change and move into the intersection is aenerally assumed to be from 4 0 to 7 0 seconds The higher values are used when pedestrian volumes are high The pedestrian clearance interval is dependent upon the width of the street being
4. 2 0 4 0 sec d 2 0 4 0 x ft s d 2 0 4 0 x ft s 10 Probability of Stopping Distance for Approach Speed Figure 13 High speed approach detection 53 An advantage of dual detection is that there are more chances of extending the green for that phase Since the phases having dual detection receive favored treatment this type of desian is most often used when the main line volumes and speeds are high as compared to those of the side street In summary if this design is encountered in a retiming situation the passage time should be set at 2 0 to 4 0 seconds The original design must be reviewed to determine the proper setting Another method of obtaining the setting is to divide the distance between the detectors by the average approach speed If there is a tendency for vehicles to slow down after crossing the second detector for example in the case of right turning vehicles the passage time may be set up to 1 0 second above the design time so that there is less chance of motorists being caught in the dilemma zone If traffic volumes at a high speed intersection are approximately the same on all approaches a volume density operation is often employed This operation was described earlier The NEMA controllers have four or five timing parameters for volume density operation three of which involve the passage time These are the time before reduction the time to reduce and the minimum gap In operation
5. kg 2 834 952 E 02 dwt 1 555 174 E 03 4 535 924 E 01 ton 2000 15 kg 9 071 847 E402 Mass per Unit Volume lb ydl kg m 4 394 185 E401 1 1 2 kg m4 2 767 990 E 04 1b ft mm kg m 1 601 846 01 lb yd kg m 5 932 764 01 Velocity Includes Speed m 8 3 048 000 01 1 m s 4 470 400 01 m s 5 144 444 01 1 609 344 E 00 Force Per Unit Area 1 1 5 6 894 757 03 1 4 788 026 Viscosity cS panna m s 1 000 000 E 06 1 000 000 01 Temperature r 32 9 C AN EVALUATION OF SIGNAL TIMING AND COORDINATION PROCEDURES Volume I Technical Report by E D Arnold Jr Research Scientist INTRODUCTION The Manual on Uniform Traffic Control Devices MUTCD defines a traffic signal as a power operated traffic control device by which t
6. Administration December 1982 The Application of Traffic Simulation Models Special Report 194 Transportation Research Board 1981 Microcomputers in Transportation Transportation Research Record 932 Transportation Research Board 1983 Microcomputers in Transportation Software and Source Book UMTA Technical Assistance Program Urban Mass Transportation Administration February 1985 STEAM As part of the Federal Highway Administration s technical assistance activities a user support group for microcomputer applications in traffic engineering has been established The following information on the services provided by this group which is called the Safety and Traffic Engineering Applications for Microcomputers STEAM User Group is summarized from its newsletter Software Exchange To increase the availability of public domain software to members of the User Group a clearinghouse has been established to distribute Federally developed software and also to collect review and distribute software contributed by members STEAM members can obtain software documentation and installation instructions at little cost Software Support Federally developed software packages and certain contributed packages are fully supported by the STEAM Support Center Full support means that the packages will be maintained by correcting errors and making enhancements Consultation and updates to users will also be provided 93 User Gro
7. G A 16 sec Check north south 5 56 4 19 sec less than 28 sec so o k east west 5 76 4 24 sec less than 31 sec so o k Verify or Adjust Timing The signal timing developed by the preceding procedures should he considered only as a starting point The procedures are based on typical traffic performance and factors at the intersection being timed may negate or modify some of the theory or assumptions used Therefore it is very important to observe the intersection in operation under the calculated timing in order to either verify the settinas or adjust them if necessary TIMING FOR ACTUATED SIGNALS AT ISOLATED INTERSECTIONS Background A traffic actuated controller operates in response to traffic demand Detectors on the roadwav advise the controller of the presence of vehicles and that particular movement or phase receives a green indication That phase retains the green as long as sufficient demand exists or until a preset maximum time has been reached Then the controller switches the areen to another phase which has been called due to the detection of a vehicle Thus within the constraints of the preset maximum times the controller provides continuously variable cycle lengths and phases in accordance with actual demand This type of control is very efficient as it allocates the right of way based on rea time demand not on the basis of an assumed demand distribution as is the case with pretimed control It is int
8. Special recognition and appreciation are extended to Mark Hodges Bob Yates and Travis Bridewell for providing information on the Department s procedures and on practical applications of the procedures Further the author is indebted to Dr Jim Hurley for his assistance with the pretimed procedures Thanks also go to the Department s district highway and traffic safety engineers for their review of the procedures and to John Shelor Steve Blackwell and Gwen Harris for assistance in analyzing the survey questionnaire Finally appreciation is extended to Jan Kennedy for typing the draft of the report to Neal Robertson for his critique and to Harry Craft and his staff for editing and preparina the final report 95 4 7 8 9 10 11 12 13 REFERENCES Cottrell B H Jr Guidelines for Exclusive Permissive Left Turn Signal Phasing VHTRC 85 R19 Virginia Highway and Transportation Research Council Charlottesville Virginia January 1985 Manual on Traffic Signal Timing prepared by the Virginia Section Institute of Transportation Engineers sponsored by the Virginia Department of Transportation Safety January 1982 Kell James H and Iris J Fullerton Manual of Traffic Signal Design Institute of Transportation Engineers 1982 Traffic Signal Manual of Installation and Maintenance Procedures 2nd ed International Municipal Signal Association Fort Worth Texas 1981 Principles of Traffic Actua
9. 475 535 1 248 Calculate Optimum Cycle Length As stated earlier the specific objective of timing a pretimed signal is to determine the cycle which minimizes average delay and will also accommodate the traffic demand One such technique Webster s Method accomplishes this through the equation GC 1 51 5 1 1 23 where C cycle length in seconds which minimizes delay at the intersection L total lost time per cycle in seconds typically 4 0 to 5 0 seconds phase and Y total of the ratios of the actual volume to the saturation volume for the critical approaches with saturation volume typically in the range 1 700 to 1 800 vph The delay at the intersection is reasonably constant in the range of 0 75 C to 1 50 C therefore a good estimate of C can still be obtained even when simplifying assumptions are made for the above equation If the lost time per phase is assumed to be 4 0 seconds and the saturation volume is assumed to be 1 800 vph then equation 1 is modiified as follows 6N 5 uis 1 800 where C as before N number of phases and CLV T sum of CLVs per phase in PCEs hr for the intersection A graphical solution to equation 2 is presented in Figure 7 and in most cases the optimum cycle can be determined directly from the graph As an example of the use of Figure 7 consider the previous example intersections A and B Intersection A has 2 phase control and a CLV of 1 190 PCEs h
10. The field method which gives a measure of stops and also an estimate of total volume is termed the Percent Stopping Study This study leads to an estimate of the number of vehicles having to make at least one stop on the intersection approach as a Percentage of the total number of vehicles entering the intersec tion The same study also gives an estimate of total volume As noted before it is recommended that the Percent Stopping Study be conducted simultaneously with the Intersection Delay Study One or two observers are assigned to the Percent Stopping Study for an intersection approach and they count all vehicles which cross the STOP line and move into the intersection during the period of study Each vehicle is classified into one of two categories and is counted only once regardless of the number of stops or amount of delay the vehicle may have suffered The two categories are stopping and not stopping By summing the two categories an estimate of total volume is obtained and can be used with results from the Intersection Delay Study to put stopped delay or approach delay on a per vehicle basis 3 Volume 1 of this report contains research findings which explain various delay types and their interrelationships Specifically the 0 92 and 0 96 modifying factors for converting field data from the Intersection Delay Study and the Percent Stopping Study respectively to accurate estimates of the true value for each measure are de
11. or the number of pedestrians is significant It is noted that other equivalency factors are sometimes used however the above factors are recommended for use with the timing procedures described later See Table 2 for a summarv of the PCE factors Table 2 Passenger Car Equivalents PCE Factors Type of Vehicle or Movement PCE Factor Trucks 6 or more tires 1 75 Intercity Buses e g Trailways Greyhound 1 75 Local Buses 5 00 Left turns with Opposing Traffic 1 75 Right turns Conflicting with Pedestrians more 1 25 than 10 right turns 16 As an example consider the case of an intersection having significant pedestrian flow and a total approach volume on one leg of 1 000 vehicles of which 10 are intercity buses and trucks 2 are local transit buses 15 are left turns and 12 are right turns The following steps illustrate the calculation of PCEs for the approach Adjust for vehicle types 1 Number of intercity buses and trucks 10 x 1 000 100 PCEs 1 75 x 100 175 2 Number of local buses 2 x 1 000 20 PCEs 5 0 x 20 100 3 Number of passenger cars 1 000 100 20 880 PCEs 1 0 x 880 880 Total PCEs 175 100 880 1 155 Adjust for turning movements 4 Number of left turning vehicles 15 x 1 155 174 PCEs 1 75 x 174 305 5 Number or right turning vehicles 129 x 1 155 739 PCEs 1 25 x 139 174 6 Number of through vehicles 1 155 174 139 842 PCEs 1 0 x 842 842 Total Approach PCE
12. the passage time of from 3 0 to 5 0 seconds determined as described previously for low speed intersections with point detectors controls the gap needed to retain the green during the time before reduction period Once this latter period times out the passage time incrementally decreases during the time to reduce period until the minimum gap is reached This gap then controls the phase until gap out or force off is attained The lower portion of Figure 14 shows gap reduction in a schematic form Note that dap reduction is initiated when a call is received on a conflicting phase Since the gap reduction feature is intended to increase the controller s response to traffic demand it is necessary that these settings be established based on field observations during the period of heaviest demand Initial settings which should be adjusted on site are generally made based on logical considerations rather than a specific methodology The main purpose of gap reduction is to make the controller increasingly sensitive to the traffic flow on the phase being serviced in recognition of the waiting time a motorist on a conflicting phase is experiencing 54 30 Seconds Maximum inital Vanable instal Range Seconds Per Actustion TIMING Seconds Minimum Green Adjustable VEHICLE ACTUATIONS EXPLANATORY DIAGRAM VARIABLE INITIAL Time Before Reduction Passage Passage Time Minimum Gap T me 10 Lev
13. with a minimum of one observer used for each method The field method which yields an estimate of delay is termed the Intersection Delay Study This technique gives an estimate of the total stopped delay see Section 2 for definition of terms in vehicle seconds incurred by vehicles passing through an inter section The study is based on a point sample of stopped vehicles Its use in traffic engineering studies was originally developed and reported by Berry and Van 1 2 The field study of delay requires a or two person team for each intersection approach and the duration of study will normally be from 13 to 30 minutes 1 Highway Capacity Manual Highway Research Board Special Report 87 Washington D C 1965 2 A Comparison of Three Methods for Measuring Delay at Intersections Proceedings California Street and Highway Conference 1954 In performing the study the field team records the number of stopped vehicles on the approach at a given instant termed the sampling point After waiting a set interval of time such as 13 seconds the team again records the number of stopped vehicles The sampling continues for the duration of the study period and the total stopped delay for all vehicles is computed as the product of the interval between samples in seconds and the sum of the number of vehicles included in the samples This product is then multiplied by a modifying factor of 0 923 to yield an estimate of stopped delay
14. 1 Locate each signalized intersection along the horizontal axis using a scale such that all intersections in the section will fit on the long axis of the sheet 1 in 60 ft and draw a vertical line at each location Identify each intersection A through E and note the cumulative distance from the beginning of the section to each intersection Write the percentage of cycle time allocated to artery green at the top of each vertical line which locates the intersection 2 Locate a vertical scale which makes 2 in equal to 80 sec 40 divisions per in and graduate the vertical line at the first intersection into 80 sec time intervals See Figure 20 3 Calculate the time T required to travel the full length of the section 5 000 ft at 25 mi h and at 30 mi h 136 sec 5000 3600 25 5280 130 5000 3600 30 5280 114 sec Draw a speed of progression line from the origin to each of these times measured along the vertical time line at the 5 000 ft location Note the speed on each line See Figure 20 78 LL uot32nJ3suo2 2 45 02 2924 Boves G BER 1 0000 T 2 p E od wee E we Pd oe E di ao orz 3 Carefully fold the cycle split aid Figure 21 vertically and crease the paper at each percentage green value shown at the top
15. 15 minute intervals would be the most accurate Figures 3 and 4 show other common forms used to summarize the data for 3 1 and 4 leaged intersections respectively Although undesirable it is possible to derive an estimate of the peak hour volume based on general relationships Generally the 12 hour volume between 7 00 a m and 7 00 p m is from 70 to 75 of the 24 hour volume and the peak hour volume is from 10 to 12 of the 24 hour volume Thus if either a 12 or 24 hour count is conducted or known then the peak hour volume can be estimated Further approximately 60 of the traffic volume during the peak hour is in the heavier direction in suburban areas In central areas the approximate percentage in the heavier direction of flow is 55 As an example of the usage of these relationships a 12 hour count at an intersection in a suburban setting shows a volume of 700 vehicles Thus the 24 hour volume can be estimated at 1 000 vehicles and the peak hour volume which generally occurs in the afternoon can be estimated at 100 vehicles Finally the two approach volumes can be estimated at 60 vehicles and 40 vehicles It is emphasized that actual traffic counts provide much better timing than counts estimated from these relationships Determine Number of Phases As a general rule the number of phases should be kept to a minimum Cycle lengths that are long result in delavs to individual groups of vehicles awaiting the green indicat
16. 475 1 248 0 38 and CLV4 CL Vr 535 1 248 0 43 Therefore from Figure 9 Entering 0 19 to the 75 sec line 6 16 sec Entering 0 38 to the 75 sec line G A 28 sec Entering 0 43 to the 75 sec line G A 31 sec and Total 75 sec 27 Figure 8 Cycle splits for 2 phase pretimed control Source Reference 2 0 0 0 2 0 3 0 4 05 0 6 0 7 0 8 0 9 1 0 Volume Ratio o Figure 9 Cycle splits for 3 phase pretimed control Source Reference 2 LL LLL LLLA 111111114 Lad LE LZ ttt Ack 2 2 mE 50 14 4 7 40 30 E 2 2 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 1 0 Volume Ratio TOT Figure 10 Cycle splits for 4 phase pretimed control Source Reference 2 It is noted that the phase times include the phase change or clearance interval Actual green time for each phase is found by subtracting that time as obtained in the next step Calculate Phase Change Interval The purpose of the phase change or clearance interval which con sists of the yellow interval and possibly an all red interval is to advise motorists of an impending change in the right of way assignment that is the commencement of a red interval on their approach Upon commencement of the change interval a motorist should have sufficient time to either stop his vehicle or clear the intersection At a given approach speed a certain amount of time is needed to decelerate to a safe stop at
17. IV AUXILIARY CONTROL EQUIPMENT STAND ALONE Type Manufacturer Model No No Units 1 Minor movement controller 2 Advance green timer 3 Pedestrian interval timer 4 All red timer 5 Railroad preemption unit IV AUXILIARY CONTROL EQUIPMENT STAND ALONE CONT D Typ Manufacturer Model No No Units 6 Fire preemption unit 7 Bus preemption unit 8 Time based coordinator for wireless system M M M P 9 Coordination unit for hard wire system 10 Other please list IV AUXILIARY CONTROL EQUIPMENT STAND ALONE CONT D Type Manufacturer Model No No Units ie 10 Other continued V DETECTORS Check the types you are using No if known Otherwise Approximate of Total Inductive loop detector ____ Magnetic detector standard Magnetometer Radar detector Sonic detector Pressure sensitive detector Other please list THANK YOU A 9 APPENDIX B A TECHNIQUE FOR MEASUREMENT OF DELAY AT INTERSECTIONS This appendix is excerpted from the user s manual which was developed as part of a research proiect conducted by JHK and Associates Definition and Measurement of Delay at Intersections The project was conducted for FHWA under contract DOT FH 11 8835 The user s manual presents an inexpensive and accurate method for measuring intersection performance The final
18. a deceleration rate in feet second usually 10 feet second W width of intersection in feet L length of vehicle in feet usually 20 feet and g percent of grade divided by 100 with upgrade being positive and downgrade being negative It is important that motorists have a reasonable expectation of the length of the yellow interval therefore the yellow interval should be set in the range of from 3 0 to 5 0 seconds Within these limits the yellow interval is often set according to the time it takes to decelerate to a stop that is the first two terms in the above equation Yellow intervals that are longer than necessary decrease capacity and encourage motorists to try to beat the light The time needed to clear the intersection as calculated by the last term in the above equation should be included in an all red interval where all approaches receive a red indication Required stopping time above 5 0 seconds should also be included in the all red interval Exclusive left turn phases do not typically have an 11 interval Normally a through movement phase follows the exclusive turn movement therefore motorists receiving the green directly face straggling left turners and can safely yield the right of way An all red interval may be needed however at a high speed intersection or at an intersection with a wide median Equation 5 minus the grade factor coupled with the aforementioned rules regarding the phase change i
19. are released in platoons or groups upon receipt of a green 62 indication and then travel in these platoons to the next signal Thus it becomes desirable to establish a fixed time relationship between the beginnina of the green interval at the first intersection and the beginning of the green interval at the second intersection such that the platoon receives the green interval just as it arrives at the second intersection This permits the continuous or progressive flow of traffic along the street When the coordinated intersections are located along a single route the term arterial svstem is applied When two or more routes cross at a common intersection the result is a signal network An open network has only one common intersection whereas a closed network has two or more common intersections This latter network is often referred to as a grid system and is commonly found in the centers of large cities Determination of the fixed time relationship becomes increasingly difficult as the number of intersections in an arterial svstem and the number of common intersections in a network increase The effectiveness of coordinated contro depends on whether traffic can be kept in platoons between intersections The ability to maintain platoons depends on traffic characteristics topography condition of the roadway and roadside friction As the distance between intersections increases the effects of these factors become more pronounced a
20. crossed and the walking speed of the pedestrian which is generally assumed to be from 3 5 to 4 0 feet second The slower speeds are used when pedestrian volumes are high or in special cases such as in the vicinity of elderly housing Thus the pedestrian clearance interval can be determined by dividing the width in feet of the street being crossed by the assumed walking speed in feet second Field measurement of walking speeds at the intersection would provide the best data The actual setting on the dial can be reduced by the vellow change and red clearance intervals as these intervals must time out before a conflict occurs It is important to remember that the intervals are set for the phase controlling traffic on the street not being crossed Verifv or Adjust Timing The signal timing developed bv the preceding procedures should be considered only as a starting point The procedures are based on typical traffic performance and factors at the intersection being timed may negate or modify some of the theory or assumptions used Therefore it is very important to observe the intersection in operation under the calculated timing in order to either verify the settings or adjust them if necessary TIMING FOR SIGNAL SYSTEMS Backaround A signal system consists of two or more signalized intersections operated in coordination that is that have a fixed time relationship to each other This relationship is based on the fact that vehicles at a signal
21. delay study Figure B 2 lines 1 and 5 are filled in on the data reduction form If two observers were used for the Intersection Delay Study it will be necessary to add the values from each of their field sheets to arrive at a total for the entire study approach if one or more point samples are missed in the field a correcting procedure is used lines a through f middle section of the data reduction form The average value for all samples taken during each period of 30 samples is used as the estimate for any missing values during that same period and is entered on line 6 lines 7 through 13 are completed as per instructions on the data reduction form itself B 3 FIGURE B 2 INTERSECTION DELAY STUDY FIELD DATA SHEET INTERSECTION DELAY STUDY POINT SAMPLE STOPPED DELAY METHOD Intersection 70507 6 224757 study Traffic on 26500 Bio City and State 4 C607 Az Agency of Tucson Pattie Engineering DIV Day Date Man Aug 2 976 Study Period 1340 1353 Observer l Mises Clear and Aor Traffic Approaching From N Weather N S E W If more than one person is studying same approach explain division of responsibilities INTERVAL BETWEEN SAMPLES 3 SECS 2 2 2 2 2 7 2010 2 2 0 187 OBSERVED TOTAL ALL SAMPLES DENOTES 30 SAMPLE UTEM See IS 3 1707209 22 seconds One sample mis
22. each signal when it is green thereby reducing the possibility of red signal violations or rear end collisions Naturally if there are fewer red intervals displayed to the majority of motorists there is less likely to be trouble because of driver inattention brake failure slippery pavement and so on 5 Greater obedience to the signal commands should be obtained from both motorists and pedestrians because the motorist will try to keep within the areen interval and the pedestrian will stay at the curb because the vehicles will be more closely spaced 6 Through traffic will tend to stay on the arterial street instead of on parallel minor streets Definitions The following definitions are applicable to timing signal systems Figure 1 depicted some of these and it has been reproduced in this section for the convenience of the reader 1 2 Timing plan a unique combination of cycle length split and offsets Cycle the time required for one complete sequence of signal indications The term background cycle is often used to identify the common cycle length established for all intersections in system Phase that part of a signal cycle allocated to any combination of one or more traffic movements simultaneouslv receiving the right of way during one or more intervals Interval a discrete portion of the sianal cycle during which the signa indications remain unchanged Split the percentage of a cycle length al
23. feature automatically returns the right of way to the minor street once the major street receives its minimum green 37 7 yellow change and all red clearance intervals are preset for each phase Full actuated Controllers Full actuated control has traffic actuations for all phases This type of control is used at isolated intersections where traffic volumes vary significantly throughout the dav and where there is not a large difference between volumes on the major and minor streets The operational characteristics were generally defined in the previous section on background Following are specific characteristics of full actuated operation 1 Detectors are located on all approaches to the intersection 2 Each phase receives a preset minimum green however the green will be extended by additional calls until a preset maximum green time is reached or until a preset gap in traffic occurs 3 The vellow change and all red clearance intervals are preset for each phase Volume density Controllers Volume density control is also fully actuated however added features enable a more comprehensive evaluation of and thus response to traffic conditions than does the basic full actuated operation The preset minimum green can be extended so as to accommodate the actua number of vehicles awaiting the right of way Likewise the preset gan which is measured in time can be reduced so as to be more sensitive to traffic flow The use
24. field observation Setting of the timing values is dependent on the controller The settings may be to the nearest whole second or to the nearest tenth of a second 40 Collect Necessary Intersection Information Basic information concerning the intersection must be obtained in order to apply the actual timing procedures described later Following is a description of the minimum data needed to calculate signal timing Effective timing is dependent upon the accuracy of the input data Control Equipment Knowledge of the control equipment already at the intersection or equipment to be installed is mandatory The controller s timing functions and their characteristics and limitations must be known In the case of equipment already at the intersection information on its timing is important to know Physical Data The following information concerning the physical dimensions and qeometrics at the intersection should be obtained 1 Number of approaches 2 Number of lanes and tvpe of flow through right turn left turn or combination per lane for each approach 3 Width of lanes and medians 4 Percent arade on approaches if severe 5 Speed limits 6 Location of parking crosswalks stop bars bus stops loading zones etc 7 location and if applicable size of detectors Traffic and Pedestrian Data Hourly traffic volumes and pedestrian counts are needed on everv approach to the intersection Further the app
25. for sale by private companies The following genera points should be made about signal timing computer programs 1 The procedures used by the computer programs are essentially the same as described in this report and thus require the same data The advantage obviously is that the procedures can be performed very quickly 2 Several of the programs have been used extensively and when used properly produce valid results 89 3 Several of the programs are available for or are being developed for use on microcomputers 4 programs do not replace the engineer rather thev provide him with a valuable tool Following are brief descriptions of several of the most commonlv known computer programs The information which is primarily from Transportation Research Circular No 282 13 is intended merely to acquaint the reader with the programs it is not comprehensive enough to allow one to determine whether the program is applicable to his specific needs SOAP 84 SOAP is a macroscopic analysis with the primary objective of developing signal control plans for individual intersections It develops cycle lengths and splits which minimize a performance index SOAP can analvze up to 48 time periods of from 5 to 60 minutes each and one intersection is simulated per run Inputs include traffic flows per approach truck and bus composition left turn data signal related data and saturation flow rates Basic outputs include dela
26. interval is dependent upon the width of the street being crossed and the walking speed of the pedestrian which is generally assumed to be 3 5 to 4 0 feet second The slower speeds are used when pedestrian volumes are high or in special cases such as in the vicinity of elderly housing 34 Except for the special situations mentioned the following general equation is applicable Field measurement of walking speeds at the intersection would provide the best data GHA in 5 W 4 6 where G A minimum green plus phase change interval in seconds on approach not being crossed and W width in feet of the street being crossed In the case of very wide streets with a median it may be judged acceptable to allow only enough time for pedestrians to safely reach the median The entire crossing would then require the timing of two cycles If the phase in question does not meet the minimum pedestrian requirements the timing should be increased to the minimum and the cycle length adjusted accordingly The previous example intersections can be used to illustrate the use of eauation 6 Intersection A north south street 28 ft 20 east west street 44 ft 6 30 north south 5 28 4 12 sec less than 30 so o k east west 5 44 4 16 sec less than 20 so o k Intersection B north south through 56 ft 6 31 east west through 76 ft 64A 28 sec east west left
27. minimum green interval for a non actuated phase is applicable to the major street at an intersection under semi actuated control on which there are no detectors to call or advise the controller of the presence of vehicles The major street is guaranteed a minimum green even if calls for service are incoming from the side street or from pedestrians If the side street demand is occasional and occurs randomly throughout the day then a relatively short setting of from 25 to 40 seconds should be used to prevent excessive delay on the side street On the other hand in a situation where the side street discharges large numbers of vehicles at certain times during the day e g from a factory with almost no demand at other times a relatively long setting of from 40 to 60 seconds is appropriate This ensures that the major street is not interrupted too frequently during the period of heavy side street demand Minimum green should be calculated based on the relative traffic volumes at the intersection To accomplish this it is assumed that pretimed control exists and minimum green on the major street or for the non actuated phase is compared with the maximum green for the side street or for the actuated phase Then the procedures for timing pretimed controllers presented elsewhere in this report should be used The green time calculated for the non actuated phase should be set on the dials for both minimum green and maximum green on that phase Other s
28. most often based on local knowledge of the traffic conditions coupled with the limitations of the controller at the intersection With the exception of information on existing controller equipment and physica data the remaining procedures apply to each timing plan needed Collect Necessary Intersection Information Basic information concerning the intersection must be obtained in order to apply the actual timing procedures described later Following is a description of the minimum data needed to calculate signal timing Effective timing is dependent upon the accuracy of the input data Control Equipment Knowledge of the control equipment already at the intersection or equipment to be installed is mandatory The controller s timing functions and their characteristics and limitations must be known In the case of equipment already at the intersection information on its timing especiallv the number of timing plans and phases is important to know Physical Data The following information concerning the physical dimensions and geometrics at the intersection should be obtained 1 Number of approaches 2 Number of lanes and type of flow through right turn left turn or combination per lane for each approach 3 Width of lanes and medians 4 Percent grade on approaches if severe 5 Speed limits 6 Location of parking crosswalks stop bars bus stops loading zones etc Traffic and Pedestrian Data In order to apply t
29. phasing if the critical number and resulting rate of left turn accidents have been exceeded For one approach the critical number is five left turn accidents one year The accident rate as defined by the annual number of left turn accidents per 100 million left turn plus opposing vehicles must exceed the critical rate determined bv the equation Rc 32 6 1 645 32 6 M 0 5 M where is the annual left turn plus opposing volume in 100 million vehicles 46 4 Site conditions consider left turn phasing if there is inadequate sight distance if there are three or more lanes of opposing through traffic if intersection geometrics promote hazardous conditions or if there are access management problems It is emphasized that the above are guidelines and should be coupled with engineering judgement More detailed information on these guidelines plus guidelines for using protected permissive phasing can be found in the above referenced report Determine Values for the Timing Parameters In recent vears traffic contro equipment has become reasonab v standardized by the National Electrical Manufacturers Association NEMA Thus the models of equipment manufactured in recent years have basicallv the same dials and settings and employ the same terminology Accordingly the following discussion on timing parameters will focus on the NEMA controllers however information on pre NEMA equipment will also be presented where possible
30. there is a common cycle length however each successive signal or group of signals along the route which are in the system shows opposite indications If each signal alternates with those immediately adjacent the progression is called single alternate If pairs of signals alternate with adjacent pairs the progression is called double alternate and so on Again this type of progression is associated with uniform spacing of the intersections Ideal spacing for single alternate progression is 0 25 mile or 1 320 feet however spacing in the range of from 1 000 to 2 000 feet is satisfactory Double alternate spacing is best suited with spacings ranging from 500 to 1 000 feet Offsets are either zero or 50 of the cycle length See Figures 17 and 18 Limited or Simple Progression Limited or simple progression also employs a common cycle length however the relationships of the indications between the intersections vary because the spacing of the intersections is nonuniform Simple progression is used where the pattern of traffic flow is relatively uniform throughout the day Offsets are different at each intersection See Figure 19 Flexible Progression Flexible progression is identical to simple progression except that the common cycle length can be changed during the day to reflect changing traffic patterns Offsets are different at each intersection and for each cycle length being used 69 FEET DISTANCE 1500 1200 900
31. timing plan and as such has no flexibility in adjusting to traffic conditions The principal disadvantage however is the inability to hold the offset relationship due to fluctuations in the power supply Whenever a controller is out of step it must be reset manually in the field Because of this problem systems of this type are not considered effective and are rarely seen in practice Time based Coordinated System The time based coordinated system is relatively new and also noninterconnected Synchronization is maintained through extremely accurate digital timing and control devices called time based coordinators at every intersection New controllers may have this function built in Time based coordinators can be programmed with a time of day and day of week schedule for implementing timing plans This allows some flexibility to adjust to traffic patterns and demand conditions however each timing plan and schedule must be set manually at every intersection in the system The main advantage is the potential savings in cost of not having to physically interconnect the controllers Also if one of the coordinators fails the remaining signals in the system maintain coordination Interconnected Master Controlled System Intersection controllers are physically connected generally through a hard wire buried in the ground or carried along overhead utility wires A variety of master controllers can implement coordination by advising the
32. 0 feet into the intersection when its presence would no longer be detected and would need only enough passage time to traverse the remaining width of the intersection Also large area detectors have a built in gap because a vehicle is detected 50 for a finite period of time as it traverses the detector This gap can be calculated by adding the length of the loop and an assumed 20 feet for the length of the vehicle and dividing by the average speed of vehicles on the approach The built in gaps for various lengths of detectors and approach speeds are given in Table 5 Accordingly when large area detectors are used at intersections having speeds of 35 mi h or less the following procedures should be undertaken to determine the passage time interval 1 Select the gan reauired to retain the areen which as discussed above shou d be between 3 0 and 5 0 sec Asa genera guideline a gap of from 3 0 to 4 0 sec is good for fast paced urban areas or where snappy operation is desired and a gap of from 4 0 to 5 0 sec is aond for slow paced rural areas 2 From Table 5 determine the built in gap for the size of the detector used and the average speed 3 Calculate the setting for the passage time interval by subtracting the built in gap from the gap required to retain the green selected in step 1 This setting is usually between 1 5 and 3 0 sec in most applications In the case of very long detectors and slow speeds the detector s bui
33. 4 3 5 2 sec green 2 east west through yellow 5 0 sec all red 1 0 sec green 22 0 sec east west left yellow 5 0 sec green 11 0 sec note the absence of an all red interval Table 3 Phase Change Intervals Total Clearance Interval Approach Yellow Change Yellow Plus All Red Clearance Speed Interval for Crossing Street Widths ft mi h sec 30 50 70 90 110 20 3 0 4 2 4 9 5 5 6 2 6 9 25 3 0 4 2 4 7 5 3 5 8 6 4 30 3 2 4 3 4 8 5 2 5 7 6 2 35 3 6 4 5 4 9 5 3 5 7 6 1 40 3 9 4 8 5 1 5 5 5 8 6 1 45 4 3 5 1 5 4 5 7 6 0 6 3 50 4 7 5 3 5 6 5 9 6 2 6 4 55 5 0 5 7 5 9 6 2 6 4 6 7 Source Reference 3 33 Check for Minimum Phase Time For safety reasons due primarily to motorists expectations there are minimum values on the timing of the phases at an intersection oper ating under pretimed control These minimums including the clearance interval are 15 seconds for through movements and 12 seconds for turning movements A quick review of the timing derived for the example inter sections will show no violation of these minimums Should these minimums be violated the phase timing should be increased to the minimum and the time added to the total cycle length Check for Minimum Pedestrian Requirements Pedestrian movements at a signalized intersection are tvpically accommodated by one of the following methods 1 Pedestrians cross the street with the parallel vehicular green indication with no pedestrian si
34. 45009 45 pz Joey gt 7 OOS i OSB J d 2 g 5 lt auf 3 OFZ 84 V 8 Now the uniform speed of progression for a platoon moving from A to E is determined by fitting a sloping straight line through the beginning of the two artery greens that will provide the highest speed of progression In the example B and E control this speed 9 The band width is the time allowed for a platoon of vehicles to move completely through the system at uniform speed and is measured on the diagram along the vertical time axis On the diagram the band width is determined graphically by fitting a line parallel to the speed of progression line through the end of the artery green that limits the band width most In the example the band width for the platoon from A to E is controlled by the end of green at A Draw the parallel line to define the band width The actual band width can be measured in seconds on the diagram with a scale 1 in 40 sec The band width is 36 sec in the example See Figure 25 10 An exact mirror image of the through traffic band from A to E can be drawn on the diagram for traffic moving from E to A The controlling times are indicated by circles on the diagram See Figure 25 This completes the construction of the time space diagram 11 Offsets for setting the signal controller at each inters
35. 5 5 4 1 3 3 2 7 2 3 2 0 1 8 110 5 9 4 4 3 5 3 0 2 5 2 2 2 0 120 6 4 4 8 3 8 3 2 2 7 2 4 2 1 Based on the formula length of detector ft 20 speed ft s and 1 mi h 1 47 ft s Table 6 Dilemma Zone Boundaries Approach Speed Distance from Intersection ft mi h for Probabilities of Stopping 10 90 35 102 254 40 122 284 45 152 327 50 172 353 55 234 386 Source Reference 6 52 Two small area or point detectors are used on each approach lane The first is placed a distance corresponding to a travel time of from 2 0 to 4 0 seconds at the average speed outside an imaginary line located within the dilemma zone at which 90 of the motorists will decide to proceed through the intersection This is the 10 probability of stop ping distance in Table 6 The second detector is placed the same 2 0 to 4 0 seconds of travel time beyond the first detector This configuration is shown in Figure 13 The passage time is then set at the same 2 0 to 4 0 seconds and actuation of either detector will cause the interval to retime itself A single vehicle traveling at the average speed will be ensured consecutive 2 0 to 4 0 second intervals which will place the vehicle at the aforementioned 90 line when a yellow clearance signal is received Likewise a single vehicle traveling above or below the average speed will find itself inside or outside the dilemma zone respectively Detector 1 Detector 2 2 0 4 0 sec
36. 600 300 CYCLE SPLIT 45 90 SECONDS PROGRESSION SPEED 1500 36 42 ft sec 28 MPH 70 30 PERCENT 63 27 SECONDS BAND WIDTH 27 sec 30 SPACING 300 FEET OFFSET 0 0 zw 29 0 90 45 90 45 90 45 90 a Time Seconds Figure 16 Simultaneous system Source Reference 2 70 Feet Distance 6000 4800 3600 2400 1200 CYCLE SPLIT 60 SECONDS PROGRESSION SPEED 1200 30 40 ft sec 27 MPH 50 50 PERCENT 30 30 SECONDS BAND WIDTH 30 Sec 50 SPACING 1200 FEET OFFSET Sec 30 50 e STREET EE 2GE RUF NOS WEM MES M 50 Ci MAIN e o 60 30 50 30 60 30 60 Time Seconds Figure 17 Single alternate system Source Reference 9 71 Feet Distance 3000 2400 bid 1200 600 CYCLE 60 SECONDS PROGRESSION SPEED 1200 30 40 ft sec 27 MPH SPLIT 50 50 PERCENT 30 30 SECONDS BAND WIDTH 15 sec 2596 SPACING 600 FEET I u 4 Band Width 7 OFFSET Sec 96 0 0 _ 30 50 _ 30 50 m 0 0 30 60 Time Seconds Figure 18 Double alternate system Source Reference 9 72 PROGRESSIVE TRAFFIC CONTROL SYSTEMS TWO WAY VS ONE WAY STREETS CYCLE SPLIT 50 50 19 3 MILES PER HOUR TIME CYCLE 30 SECONDS WAY STREETS THROUGH BAND 100 OF GREEN INTERVAL PASADENA ATLANTA ST _ _ m _ _ TWO WAY STREETS THROUGH GANO 50
37. 70 70 0 34 20 55 15 i 35 6 50 20 off 70 70 0 35 35 430 off 65 35 6 100 70 30 OA DA A 8 65 30 or ss 06 4 o D m 4 35 50 15 The final designator of 30 65 means that our offsets have given start of green at along AB that is 30 seconds too late or 40 seconds too soon We choose the smaller of the two and adjust our offsets to move traffic around the network 30 seconds faster Adjusted offsets 0 35 14 41 0 14 off 5 T 14 8 20 eM 35 G 49 49 21 off 35 70 84 70 70 0 14 2 o X 35 G 2 2 14 44 14 35 0 14 off 21 off Check new speeds 49 M 35 zm 35 G t AB and CD 600 ft 43 fps 29 mph 84 35 14 sec 70 BC and DA 900 ft 43 fps 29 mph m5 270 21 sec P mp 0 So a required C 70 will result in speeds higher than the desired 20 mph 5
38. IRR DE UN cc p pq qo dodo du d b Li qao og de tt tT EE EET ee ee IESU Ze 0 0 0 Berge BEBE NI ee OO TOTAL ERE GR ER ERR RE EN TOTAL RECORDED BY SUPERVISOR Figure 2 Typical data collection form 43 EIGHT MAXIMUM HOUR VOLUMES OF APPROACH VEHICLES TIME M TOTAL PED PED PED PED ze rl Baur za Figure 3 Typical data summary form for three legged intersection 44 EIGHT MAXIMUM HOUR VOLUMES OF APPROACH VEHICLES PED PED PED PED j PED dE ve IE RES ie ris p oed SEC ole Figure 4 Typical data summary form for four legged intersection 45 Determine Number of Phases As a general rule the number of phases should be kept to a minimum Cycle lengths that are long result in delays to individual groups of vehicles awaiting the green indication therefore there are practical limits to cycle lengths in order to avoid these intolerable delays Accordinglv additional phases tend to decrease the available green time for other phases since they must be accommodated within the practical maximum cycle length Also there is additional lost time through start up delays and phase change or clea
39. It is very important to be familiar with the timina functions of the equipment being retimed or being considered in the case of a new installation The phase timing for a NEMA traffic actuated controller is shown in Figure 11 and a typical phase timing for older equipment is shown in Figure 12 Both of these fiqures are referenced in the following discussion of timina parameters The following general rules concerning the timina of traffic actuated controllers are often cited These are contained in the International Municipal Signal Association s Traffic Signal Manual 4 1 Make all timing adjustments during heavy traffic The controller will then automatically take care of the light traffic efficiently 2 Set the dials at values considered correct after evaluating detector spacing relative volumes and desired results Then adiust or tune the controller to accommodate the heaviest traffic 3 After the dials have been set take steps to ensure that unauthorized persons cannot change them 4 tendency is to set the times too high In general lower settings produce snappier more efficient intersection operation Timing parameters must be established for each phase 47 J int al State Detector Actuation on Phase with Right of Way The Initial State is the minimum nght of way time It wil be the Minimum Green time the Passage time the Added Initial time in Volume Density appl
40. ORY OF EQUIPMENT oves in TIMING FOR PRETIMED SIGNALS AT ISOLATED INTERSECTIONS TIMING FOR ACTUATED SIGNALS AT ISOLATED INTERSECTIONS TIMING FOR SIGNAL SYSTEMS Ga SIGNAL TIMING COMPUTER ACKNOWLEDGEMENTS ELT LETTE ee ree Tr APPENDIX INVENTORY OF SIGNAL EQUIPMENT IN VIRGINIA APPENDIX B TECHNIQUE FOR MEASUREMENT OF DELAY AT INTERSECTIONS mda ds ra Ed wae ew ES EET E APPENDIX C CALCULATIONS FOR NETWORK COORDINATION iii 36 63 89 95 97 A 1 ABSTRACT Based on a review of available literature recommended procedures for timing the various types of signals are provided Specifically procedures are included for both pretimed and vehicle actuated controllers located at isolated intersections and at intersections in a signal system Simplicity and ease of use are emphasized as the targeted users are field technicians and those responsible for signals in small cities and towns A separate Field Manual has been prepared which is intended to provide a concise and easily applied set of procedures Detailed theory and logic behind the procedures are provided in the Technical Report as are brief descriptions of current computer programs which provide timing information The Technical Report also presents the results of a questionnaire su
41. R gt lt gt lt auoqsyoe ld deg 15 pueTysy 24 gt lt gt lt X 5 xXx gt lt gt lt gt lt X gt lt IS gt lt gt lt gt lt oloqsaukem yoeag eA ATOTINS uoquneis 101504 u3nog ayouroy ee PRENNE Mu n a _ gt uosonbog ATOJION SMAN J10dman 1 SPS x 24 24 uo3j2urxe1 gt 24 56 54 25 gt d DE OG gt lt OS OS OS 8 83104 11110 ayeodesay x x X X x x X uoJ3u1T y ooriueH 34suel L 5 129385 X3NOOVHL SOTUOSTITNY a9 I 818 eiuLBJLA UL 54941044 09 LeUBLS 40 SJaJnj5egnuey 2 1 0 OFFFeAL saljuno 9 94 18 Auxiliary Equipment Tn recent years the functions performed by auxiliarv stand alone equipment have been incorporated into the signal controller itself The Virginia Department of High
42. X OF GREEN INTERVAL o A dE M ap Wr sT ATLANTA Figure 19 Progressive system Source Reference 2 73 Objective The major objective of signal timing is to assign the right of way to alternate traffic movements so that all vehicles are accommodated with a minimum amount of delay to any single group The specific objective of a signal system is to facilitate movement of vehicles through a series of signalized intersections This is accomplished by coordinating the individual intersections in the system primarily through the establishment of fixed time relationships between intersections Timing Procedures Timing procedures for signal systems become very time consuming and complex once simple system configurations are exceeded In recent years computerized procedures for timing systems have been developed and a separate section of this report presents summary information on the most common of these programs Manual techniques are useful for relatively simple systems and when a computer is not available and these are presented in the remainder of this section Specifically procedures for the following types of systems are discussed Arterial system 1 Uniform block spacing two directional flow Cycle length not predetermined Cycle length predetermined 2 Nonuniform block spacing Two directional flow One directional flow Signal network 1 Open network 2 Closed network It is impor
43. ansportation Research report entitled Adding Signals to Coordinated Traffic Signal Systems 11 Uniform Block Spacing Two directional roe Cycle Length Not Predetermined The following methodology is used when a street that is not part of any other system and when the cycle length is restricted only by the traffic requirements at individual intersections along the route 1 Select a desired speed of progression for the system 2 Compute the time required to travel one block at the desired speed 3 Select a single double or triple alternate system on the basis of time required for a round trip from the first intersection to the second third or fourth intersection If a round trip to the second intersection results in an acceptable cycle length that satisfies the traffic requirements at all intersections use the single alternate system if the trip to the third intersection and back gives a good cycle length use the double alternate system if the round trip to the fourth intersection gives a better cycle length use the triple alternate system 75 Example Uniform block spacing of 400 ft Desired speed of 25 mi h 25 mi h 36 7 ft s 400 ft Travel time per block 10 9 sec 36 7 ft s Round trip to second intersection 21 8 sec Round trip to third intersection 43 6 sec Round trip to fourth intersection 65 4 sec In this example a double alternate svstem with a 45 sec cycle length would be us
44. are actuated approximately 20 operate semi actuated 50 operate fully actuated and 30 operate fully actuated with volume density timing On the other hand local jurisdictions espe cially small cities and towns maintain a significant number of pretimed Signals Seventeen percent of the isolated intersections are under pretimed control whereas 26 are semi actuated 48 are fully actuated and 9 are fully actuated with volume density timing Signal Systems The Department maintains 46 systems all of which are arterial systems Approximately 200 intersections are included in these systems and the majority of these operate semi actuated Twenty six of the systems utilize time based coordinators whereas the other 20 are hard wired through a street master controller Local jurisdictions reported a total of 82 systems with 919 intersections Sixty three are arterial systems Fifty nine percent of the intersections in the systems operate pretimed 25 operate semi actuated 13 operate fully actuated and 3 operate fully actuated with volume density timing Only 13 are coordinated through time based coordination the remaining 87 have hard wire interconnection Eightv two percent of the interconnected systems are controlled by a street master 14 by a central computer and 2 by a time clock guuarA TTTH 11006 spuequory 210014 gt P
45. artery green remains to accommodate a platoon from A This is within the tolerable speed range therefore centering artery red is accepted for defining the offset at this intersection Draw bars on the diagram at B with red centered on the time reference line to indicate the red intervals on the arterv If green is centered on the time reference line only a few seconds of artery green will remain for the platoon from A and a very narrow band width would result This is therefore not an acceptable offset See Figures 22 and 23 Repeat the procedure described in 6 above for each signalized intersection in the system Either artery red or artery green must be centered on the time reference line The decision as to which is based on the objective of allowing an acceptable speed of progression with a maximum band width a function of the end of artery green See Figure 24 80 PERCENT GREEN 70 20 10 30 50 60 90 80 Cycle split aid Figure 21 Source Reference 11 BUI 22024242 21 LL 92u848j48y UOLZONUZSUOD adeds auty 22 aunb y Z 2 spuosas dwl 3 ofc 82 11 92u848j94 2924005 001391235009 45 EZ 2929 07 COVE 088 2 o _ 2 g ee 467 32U24242 ZU pF o dwt 7 P d 3 g P 0 3 v 029 o9 09 83 11 923u8489j894 894N0S 0013914
46. aster controller _ Central computer ___Time based System No 6 Check all applicable descriptors Type of system ___ Grid network Arterial Type of controllers ___Pretimed Semi actuated __Fully actuated ___Volume density Type of interconnect Comments Hard wire dow coordinated __Street master controller Central computer lime based Me III SIGNAL CONTROLLERS IN A SYSTEM CONT D System No amp Description Manufacturer Model No No Units System No 7 Check all applicable descriptors Type of system ___Grid network Arterial Type of controllers __Pretimed __Semi actuated Fully actuated Volume density Type of interconnect Commen ts Hard wire How coordinated Street master controller Central computer Time based System No 8 Check all applicable descriptors Type of system Grid network Arterial Type of controllers Semi Fully actuated ___Volume density Type of interconnect Comments Hard wire How coordinated Street master controller Central computer Time based System No 9 Check all applicable descriptors Type of system ___Grid network Arterial Type of controllers Pretimed Semi actuated ___Fully actuated ___Volume density Type of interconnect Comments ___Hard wire How coordinated Street master controller computer Time based
47. controller Central computer ___Time based System No 2 Check all applicable descriptors Type of system ___Grid network __Arterial Type of controllers ___Pretimed ___semi actuated ___Fully actuated ___Volume density Type of interconnect Hard wire How coordinated Street master controller Central computer Time based System No 3 Check ail applicable descriptors Type of system amp rid network Arterial Type of controllers Pretimed Semi actuated ___Fully actuated ___Volume density Type of interconnect Hard wire Bow coordinated Street master controller ___Centra computer ___Time based Manufacturer Model No Comments Comments Comments No Units III SIGNAL CONTROLLERS IN A SYSTEM CONT D System No amp Description Manufacturer Model No No Units System No 4 Check all applicable descriptors Type of system ___ Grid network Arterial Type of controllers ___Pretimed ___Semi actuated Fully actuated Volume density Type of interconnect Commen ts Hard wire How coordinated Street master controller Central computer ___Time based System No 5 Check all applicable descriptors Type of system Gri d network Arterial Type of controllers Pretimed Semi actuated ___Fully actuated Volume density Type of interconnect Comments Hard wire How coordinated ___Street m
48. ctuated equipment are described in the following subsections Semi actuated Controllers The best use of a semi actuated controller at an isolated intersection is where the major street volumes are high compared to the minor street volumes The major street phase is not actuated therefore the right of way always returns to the major street when there are no vehicles present on the minor street or when the minor street s maximum green time has been reached This type of operation is also used where the controller is incorporated into a siqnal system The non actuated phase is coordinated with adjacent intersections while the actuated phases are allowed to respond to detected demand within certain limitations Following is a list of characteristics of semi actuated control 1 Detectors are located on only the minor street approaches to the intersection 2 major phase or non actuated phase receives a preset minimum qreen interval 3 major phase green extends indefinitely until interrupted bv a call from the minor street 4 minor phase receives a qreen indication after it is called if the major phase has completed its minimum areen interval 5 minor phase receives a preset minimum green however the green will be extended by additional calls until a preset maximum green time is reached or until a preset gap in traffic occurs If the time is terminated the preset maximum a memory
49. delay to any single group of vehicles Short cycle lengths minimize average delay or delay to single groups of vehicles provided the capacity of the cycle to pass vehicles is not exceeded If there is a constant demand however long cycles will accommodate more vehicles over a given period of time because there is a lower frequency of starting delays and clearance intervals between phases Satisfying the objective of signal timing therefore results in conflicting requirements for the cycle length Thus the objective should be restated to that of determining the shortest cycle length which will accommodate the traffic demand within certain limits Timing Procedures A summary of the recommended procedures for timing a pretimed signal is listed below The basic concepts for each step along with appropriate examples of using the procedures are described in the remainder of this section Because of the relationships among physical data type of equipment timing plans and phasing it may be necessary to undertake steps 1 through 3 simultaneously if a new signal is being installed 1 Determine the number of timing plans needed 2 Collect necessary information at the intersection 3 Determine number of phases needed 4 Calculate passenger car equivalents 5 Find critical lane volumes 6 Calculate optimum cycle length 7 Calculate cycle splits 8 Calculate phase change interval Check for minimum phase time 10 Check
50. does not receive a full passage time interval because of being forced off or an actuation is received during the yellow change interval the controller assumes the vehicle did not clear the intersection Thus the green is automatically returned to that phase at the earliest opportunity On the other hand if a gap in traffic is large enough such that the passage time is reached before being re actuated then the phase ends and the controller switches to another phase that has been called This is often called a gap out Accordingly the passage time has two functions it allows vehicles to travel from the detector through the intersection and it establishes the gap measured in seconds at which green is terminated At intersections where speeds are 35 mi h or less and where small area or point detectors are used the needed passage time is calculated by dividing the distance between the intersection and the detector by the average approach speed of traffic However the gap required to retain the green must also be considered Bumper to bumper traffic produces gaps of from 2 0 to 3 0 seconds with the former being indicative of fast paced urban areas and the latter being more likely in rural areas Passage times set in this range make the operation too sensitive to gaps On the other hand gaps greater than about 5 0 seconds cater to the stragglers in the traffic stream and cause a reduction in efficiency Detectors are typically located suc
51. e vph 831 710 1 036 948 Figure 6 948 Va CE a E Bn al Passenger Left Cars Trucks Turns vph vph 2 748 83 12 625 85 14 995 41 19 891 57 24 Pedestrians minimal Buses none V Control 3 phase pretimed Approach speed 45 mi h north south Approach speed 55 mi h east west Example intersection B Source 21 Reference 2 Phase 1 East West Left Turns Trucks as PCEs Passenger cars Tota Left turn traffic 1 Eastbound 1 75 41 72 995 1 067 9 x 1 067 203 CLV Phase 1 238 PCE hr factor not applied since are unopposed Phase 2 East West Through and Right Movements Trucks as PCEs Passenger cars Total Through and right turn traffic Citical lane traffic Eastbound 1 75 41 72 995 1 067 81 x 1 067 864 55 x 864 CLV Phase 2 475 PCE hr 22 475 Westbound 1 75 x 57 24 x 991 left turns Westbound 100 891 991 238 1 75 x 57 100 76 x 991 55 x 753 891 991 753 414 Phase 3 North South Movement Trucks as PCEs 1 75 x 83 145 1 75 x 85 149 Passenger cars 748 625 Total 893 774 Left turn traffic 12 x 893 107 14 x 774 108 Left turns as PCEs 1 75 x 107 187 1 75 x 108 189 Through and right turn traffic 88 x 893 786 86 x 774 666 Total approach PCEs 973 855 Critical lane traffic 55 x 973 535 55 x 855 470 CLV Phase 3 535 PCE hr CLV Total 238
52. e band width in both directions for up to 20 intersections A modified version of Webster s delay equation is used to approximate platoon effects Basic inputs include the range of cycle lengths movement flows saturation flows left turn patterns queue clearance times desired speeds minimum green times allocation of band width by direction cross street phase sequences and intersection distances Outputs include cycle length band widths band speeds a time space diagram delav probabilitv of queue clearances offsets splits phase sequences and volume to capacity ratios Its main advantage is its flexibility to vary cycle lenath and band speed and its ability to consider multiphase operation under a variety of sequencing strategies Other advantages are ease of input and low run times The main disadvantage is its use of band width as its optimization criterion Also it does not accommodate closed networks and fuel consumption and emissions are not included It has been used extensively and is available for the micro PASSER II 84 is also available PASSER III PASSER III produces the cycle length splits and phasing sequence for a pretimed diamond interchange that minimize average delav per vehicle using a macroscopic deterministic time scan optimization Tt can also determine splits and offsets for interchange signals along frontage road using a band width procedure Inputs in addition to those required for PASSER II 80
53. earest whole number Total value for all missing samples in JO sample period b x d f Total value for all missing samples in study period sum of e for all corrections Use one correction factor for each 30 sample period in which the field data sheet has one or more missing values INTERSECTION DELAY STUDY 1 Total no of point samples taken in field 2 Total no of point samples missed from b above Total no of point samples used in calculations 1 2 Interval between samples Sum of observed point sample values Sum of calculated correctad point sample values from f above Sum of all point sample values 5 6 Total Stopped Time 4 x 7 Stopped Delay 8 x 0 925 Approach Delay 9 x 1 35 Total Volume iii Stopped Delay Per Vehicle 9 11 Approach Delay Per Vehicle 10 11 5 See footnote 3 page 2 0f this manual for comment on these modifying factors B 11 6 PRESENTATION OF RESULTS The measures which can be estimated from the Intersection Delay Study and the Percent Stopping Study are note that line numbers refer to data reduction form Percent Stopped line v Stopped Delay in vehicle seconds line 9 Approach Delay in vehicle seconds line 10 Stopped Delay Per Vehicle vehicle seconds per vehicle line 12 Approach Delay Per Vehicle in vehicle seconds per vehicle line 13 The latter two measures require a volume count for
54. ection can be scaled from the diagram with adequate precision for practical purposes but they can also be calculated from the relative time values shown on the diagram Nonuniform Block Spacing One directional Flow Progression for one directional flow is applicable in systems on one way streets or where there is heavy directional flow on the artery in the morning and evening peak periods The procedure is to offset the beginning of the artery green at each intersection such that it coincides with the arrival of the lead vehicle in a platoon traveling on the artery at the desired progression speed Traffic in the other direction may or may not experience progression through the system The construction of a time space diagram for the case of one directional flow is illustrated in the steps below Before beginning however the cycle length and splits are determined as they were for two directional flow Likewise the speed of progression must be specified 1 basic layout for a time space diagram is prepared with all signalized intersections located along the horizontal scale 85 LL 92u849j8y4 ueJberp 45 2 39 4 f gt gt 275 17 COTE J gg 9Jnbi4j 088 2 09 g 259 26 41 4 Speo ss OFZ OG 86 A construction line is drawn across the diagram with a slope equal to the desired speed of progression This line is the bottom
55. ed if the 45 sec cycle satisfies the traffic conditions at the individual intersections 4 offsets for all signals would be either zero or one half the cycle length For example in a double alternate system with a 45 sec cycle the first two intersections would have zero offset the next pair 22 5 sec offsets the next pair zero etc Non signalized intersections are included when determining offsets 5 The division of the cycle length i e green yellow and red intervals for individual intersections is obtained by ana lyzing each case Thus although the beginning of the green interval is synchronized to provide coordinated flow the end of the green interval may present a slightly irregular pattern 6 The through band width depends on the system that has been selected For a single alternate system the width of the through band is equal to the shortest green plus yellow period for a double alternate the width is one half the green plus vellow and for the triple alternate the width is one third the qreen plus vellow The triple alternate should be used sparingly because of the reduction in the efficiency of the system Uniform Block Spacing Two directional Flow Cycle Length Predetermined The following methododology is used when the cycle length is predetermined e g one intersection may be part of an intersecting coordinated system 1 Obtain block spacina and cycle length 76 2 Determine speed of progr
56. ei 1 1 E 1 1 Slope Rate of Reduction 2 ti 5 Passege Time Minimum Gap T Time to Reduce 11 a 11 9 m z Time to Reduce i t 10 Minimum Gap Time Level en r Time 19 Reduce 14 7 Aeguatration of Serviceable Contlicting Cau eque t t REAL TIME Seconds 0 Start of Phase Green tg and 14 may start simuiteneously Passage time portion of Green Interval must time concurrently with variable Initial subject to vehicle actuations EXPLANATORY DIAGRAM GAP REDUCTION Figure 14 Volume density timing functions NEMA Source Reference 2 55 The controller is most sensitive to traffic flow when operating with the minimum gap and should maintain green only during bumper to bumper traffic Thus a minimum gap setting of from 2 0 to 3 0 seconds will usually be effective If the phase being considered is relatively minor then the time to reduce can be rather short e g 15 to 20 seconds On the other hand the time to reduce on a major phase may be set at 30 seconds or more The time before reduction is useful in delaying gap reduction until slow moving traffic such as large trucks can get in motion Another general rule of thumb is that the minimum gap should be reached by the time the phase is at 80 of its maximum green time The split between time before reduction and time to reduce can be determined according to the general logic jus
57. eresting to note that when the traffic flow is heavy for al movements the actuated controller functions in pretimed operation with the cycle length and phase times being governed by the preset maximum times Definitions The following general definitions are applicable to timina actuated signals 1 Cycle the time required for one complete sequence of signal indications 2 Phase that part of siqnal cycle allocated to combination of one or more traffic movements simultaneously receiving the right of wav during one or more intervals 3 Detector a device which detects the or presence of a vehicle with the purpose of advising a controller of the need for a green indication For purposes of this project detectors will be categorized as either small area detectors or large area detectors Small area detectors provide passage point motion or unit detection These detectors simply register the passage of a vehicle It is noted that a 6 x 6 foot loop is often used as a point detector Large area detectors provide presence or area detection These detectors 36 register the presence of a vehicle in the zone of detection As will be discussed later the timing can vary with the type and location of the detectors 4 Gap distance between successive vehicles crossing a point on the roadway For signal timing the distance is usually measured in seconds Types of Equipment The three distinct tvpes of a
58. es stopping Total no of vehicles not stopping et ee wt te s Total volume 44 Observed Percent Stopping o aa x 100 Se ed Actual Percent of Vehicles Stopping iv x 0 96 CORRECTION PROCEDURE POR MISSED SAMPLES IN DELAY STUDY a b 4 Total no of point samples taken in field during 30 sample period 30 a 6 6 9 9 c b h 9 e e 9 4 s Sum of point sample values for 30 sample period on field data sheet Value of each missing sample c a round to nearest whole number Total value for all missing samples in 30 sample period b x d Total value for all missing samples in etudy period sum of for all Use one correction factor for each JO sample period in which the field data sheet has one or more missing values INTERSECTION DELAY STUDY a 2 3 4 5 6 7 8 9 10 11 12 13 Total no of point samples taken in field Total no of point samples missed from b above eee Total no of point samples used in calculations 1 2 Interval between samples EA ee ee ee Sum of observed point sample values 444 4 4 Sum of calculated corrected point sample values from f above Sum of all point sample values 5 6
59. ession by dividing the block spacing by one half one fourth and one sixth of the cycle length respectively for single double or triple alternate systems Example Uniform block spacing of 400 ft Cycle lenath of 50 sec 400 ft Single alternate 16 ft s or 10 9 mi h 250 sec 400 ft Double alternate 32 ft s or 28 0 mi h 1 50 sec 400 ft Triple alternate 48 ft s or 32 7 mi h 2 50 In this example a double or possibly triple alternate system would be used depending on the desired speed Nonuniform Block Spacing Two directional Flow A time space diagram is used to develop a timing plan for a system with nonuniform block spacing Before the diagram can be constructed however the background or common cycle for the system and the needed splits at each intersection must be determined Normally the cycle required to handle the traffic at the highest volume intersection in the system is chosen as the background cycle For pretimed intersection the optimum cycle length is calculated as described in the previous section on pretimed signals at isolated intersections In the case of actuated control the intersection is considered to operate at maximum loading or in a pretimed manner and thus the cycle length is also determined as described previously for pretimed control Once the cycle length is determined the splits are then calculated as described under pretimed control Again actuated signals are assumed
60. ettings are determined based on the actuated signal procedures Maximum Green The maximum green interval determines the longest time that continuously moving traffic can hold the green signal once a call has been received on a conflicting phase In operation when gaps in the traffic flow are sufficiently small to cause the passage time interval to continuously retime itself the green is forced off because the maximum value is reached rather than because the gap required to retain the green is exceeded If the passage time has been set correctly the force off condition is attained only during times of heaviest traffic flow at the 58 intersection As mentioned previously the controller is operating essentially in a pretimed fashion during heavy flow conditions because all phases are being forced off at the preset maximum times Accordingly the maximum green per phase for actuated control should be determined in the same manner as the green time per phase is determined for pretimed control The reader is referred to the section of the report on pretimed control Figures 11 and 12 depict schematically how the maximum green is timed As shown in Figure 11 the maximum green for NEMA controllers begins timing upon receipt of a call on a conflicting phase As shown in Figure 12 the maximum interval for older controllers begins after the initial interval has timed out While it is not critical to take these differences into account when setting
61. f the intersections It is also used to manually determine offsets and the progressive flow characteristics See Figure 15 Progression or band speed the speed which a platoon needs to travel in order to progress or continue from intersection to intersection in the system without being stopped It is the slope of the band lines in Figure 15 Band band width or through band the amount of time in seconds between the first and last vehicles traveling at the band speed which can progress through the system without stopping The efficiencv of the timing plan is often measured by the band width as a percentage of the cycle length See Figure 15 65 Phase Main St Second St Red Yellow Phas 2 Interval Interval Interval Figure 1 Timing sequence for simple two phase controller BANOWIDTH TIME CYCLE DISTANCE A Figure 15 Time space diagram Source Reference 8 66 Types of Systems In addition to the broad categories of arterial and grid systems described earlier the Traffic Control Devices Handbook 6 categorizes systems according to the type of hardware components These categories are described in the following subsections Noninterconnected Svstem In a noninterconnected system the controllers or coordinating units are synchronized through the 60 hertz cycle of the area s power supply This type of system is usually limited to a simple
62. for minimum pedestrian requirements 11 Verify or adjust timing after actual field observation Setting of the timing values is dependent on the controller The settings may be in percent of cycle to the nearest whole second or to the nearest tenth of a second Determine Number of Timing Plans The maximum number of timing plans is determined by the tvpe of controller The typical three dial electromechanical controller can provide for three independent timina plans one per dial The modern microprocessor based controller is generallv capable of a total of 1 plans a combination of at least four cycles and three splits The variation or pattern of traffic demand at an intersection determines the number of plans Traffic demand patterns are tvpically categorized as a m or p m peak period average or midday period late night or low volume period weekend period shopping period evening period or special function period Within the capabilities of the controller each of these well defined periods would normal v receive a separate timing plan It can generally be assumed that a minimum of two plans are needed one for peak conditions and one for off peak conditions Two plans are often needed for peak condition inbound peak and outbound peak Extensive traffic counting may be undertaken to evaluate the daily or weekly variations in traffic demand in order to determine the number of timing plans needed However this determination is
63. gnals 2 Pedestrians cross the street with the parallel vehicular green indication as instructed bv special pedestrian siqnals 3 Pedestrians cross the street on an exclusive phase when all vehicular traffic is stopped For any of the above methods sufficient time must be provided for pedestrians to enter the intersection called the walk interval and to safely cross the street called the pedestrian clearance interval In the first two cases above the time needed for pedestrians occurs while the parallel vehicular traffic or traffic on the street not beina crossed is receiving a green and clearance interval Therefore the sum of the green and clearance interval for an approach should be long enough to accommodate anv pedestrian flow on the cross street In cases the combination of pedestrian and vehicular volumes may not create enough conflicts to warrant a check for the minimum time needed by pedestrians At locations where there are significant pedestrian volumes or pedestrians require special attention such as near elderly housing it is necessarv however to calculate the needed crossing time and compare it with the time allocated to the movement of parallel vehicular traffic The walk interval or time needed hy e pedestrian to perceive the signal change and move into the intersection is generally assumed to be from 4 0 to 7 0 seconds The higher values are used when pedestrian volumes are high The pedestrian clearance
64. h that the passage time falls in this range Therefore the passage time interval at intersections where speeds are 35 mi h or less and point detectors are used should be set to the nearest tenth of a second as calculated by dividing the detector spacing by the average approach speed however it should be no less than 3 0 seconds and no more than 5 0 seconds Table 4 summarizes these rules 49 Table 4 Passage Times for Various Point Detector Spacings and Speeds Average Approach Distance Between Stop Bar Passage Time Interval Speed mi h and Detector d ft sec 15 0 67 3 0 68 108 d 22 0 more than 108 5 0 20 0 89 3 0 90 145 d 29 3 more than 145 5 0 25 0 111 3 0 112 181 d 36 7 more than 181 5 0 30 0 134 3 0 135 217 d 44 0 more than 217 5 0 35 0 156 3 0 157 253 d 51 3 more than 253 5 0 40 0 179 3 0 180 290 d 58 7 more than 290 5 0 45 0 201 3 0 202 326 d 66 0 more than 326 5 0 In slow paced rural areas the passage time may have to be set higher than the recommended minimum of 3 0 seconds Also if the detectors are placed such that the needed passace time is areater than 5 0 seconds it may be necessary to set the passage time interval above the recommended maximum for safety purposes Doing this will decrease the efficiency of the intersection If large area or presence detectors are used at the stop bar very little time is needed for a vehicle to clear the intersection For example a typical vehicle would be about 2
65. he timing procedures described later hourly traffic volumes and pedestrian counts are needed on every approach to the intersection Further the approach traffic should be categorized into the number of vehicles turning left going straight through and turning right It is also necessary to count and record the number of buses and large trucks per hour on each approach Finally the average speed of traffic approaching the intersection on each leg should be obtained 10 This hourly information is needed for each timina plan determined earlier For example a three dial controller may have a timing plan for the morning peak period a lunch or midday period and an afternoon peak period In order to calculate the timing for each plan the above described hourly information representative of these three periods must be obtained Likewise traffic and pedestrian data for weekends nights and special functions must be obtained in order to calculate the timing for these periods It is noted that data collected on Tuesdays Wednesdays and Thursdays are more representative of average weekday conditions than those collected on Mondays and Fridays A typical data collection form is provided in Figure 2 It is noted that the volumes are tabulated by one half hour intervals during the normal mornino and afternoon rush hours This enables a more accurate determination of peak hour statistics than would be possible with one hour summaries Volume counts by
66. ications Unexpired Portions of or the sum of the Walk and Pedestrian Passage Time Period Clearance ume whichever 15 longest Optional Red Clearance Yellow 4 Maximum Time Last car did not receive End ot Green Passage period so green light will be automatically returned Detector actuated on at first opportunity another phase at this point starts maximum timing Start of Green Figure 11 Typical timing diagram for a full actuated NEMA controller Source Reference 5 Maximum Interval Initial Vehicle Reset Interval Interval Vehicle Intervals Minimum Green Time UG Model 804N Timing Diagram Cancelled Portions of Vehicle Intervals Figure 12 Typical timing diagram for a full actuated non NEMA controller Source Reference 2 48 Passage Time For the typical low speed intersection the passage time which has also been referred to as the vehicle interval or unit extension interval is defined as the time needed for a vehicle moving at average speed to travel from the detector to and through the intersection As shown in both Figures 11 and 12 this interval begins to retime itself when a vehicle actuates the detector Retiming continues upon each actuation until such time as the maximum time setting is reached then the controller switches to another phase that has been called This oper ation is referred to as force off or max out If a vehicle
67. include the interchange description for the isolated case and interchange spacing and progressive speed for the progression case Outputs include signal settings plus value for delav dearee of saturation etc For the progression case band width speeds efficiency and time space diagrams are provided The main disadvantage is its use of band width as the progression criterion 91 SIGOP SIGOP produces the cycle length splits and offsets of signals in a grid network that minimize a delay in disutility function by using a macroscopic traffic flow model It can handle up to 150 intersections Inputs include arrival flows and saturation flows in terms of headwavs minimum green times yellow times special phase times and passenger car equivalent factors for trucks buses and turning vehicles Outputs include time space plots along selected arterials and link statistics Signals with up to four phases can be modeled Disadvantages include run times for large networks that are no shorter than other programs and SIGOP III the latest version lacks extensive field testing TRANSYT TRANSYT produces splits and offsets for signals in a network that minimize a performance index using a hill climbina procedure and a macroscopic deterministic flow model Its dimensions are usually set to handle up to 50 intersections and 300 links Numerous versions of the program have been produced both by its originator and others Tn most vers
68. ing traffic may still travel through the system but it will be stopped at one or more signals 87 Time space diagram for Main Street evening peak hour 60 second cycle Time in sec KE A Time scale one cycle length Distance i in ft Main Street te aes duh 00 SS rm rt 50 UB S cs CU em D Se E Sc St G St MH St a Sto St UK St CU St UM St UN St 0 50 SCIO St St Figure 26 Completed time space diagram favoring one direction of flow Source Reference 10 Signal Network The procedures described thus far relate to systems along a single route As discussed previously if two or more routes cross at a common intersection the result is a signal network Open Network An open network contains only one common intersection and in general the cycle length for the network is fixed by the requirements at this common intersection The cycle length and splits at the common intersection are determined as described previously for pretimed control at isolated intersections This cycle is then used to calculate the splits at all other intersections in the network again using the 88 previously described procedures for pretimed control Development of the timing plan for each route then proceeds independentlv as described for arterial systems that is a progression speed is specified and the appropriate time space diagram
69. ion therefore there are practical limits to cycle lengths in order to avoid these intolerable delays Accordingly additional phases tend to decrease the available green time for other phases since thev must be accommodated within the practical maximum cycle length Also there is additional lost time through start up delavs and phase change or clearance intervals over the course of a cvcle as the number of phases increases 11 DIRECTIONAL TRAFFIC MOVEMENT INTERSECTION OF ROUTES _ _ _ COUNTY LOCATION DATE LL L ee WEATHER APPROACHING INTERSECTION FROM ON FROM THE ROUTE THE RECORDED BY SUPERVISOR Figure 2 Typical data collection form 12 E qp o ior dap lli ql cl rp du i me Figure 3 Typical data summary form for three legged intersection 13 Figure 4 Typical data summary form for four legged intersection 14 The number of phases required at an intersection is most often a left turn issue As the volumes of left turn and opposing traffic increase it becomes more difficult for the traffic turning left to find adequate gaps A separate left turn lane can alleviate the problem to some degree by providing storage for vehicles awaiting an adequate gap however at a certain point a separate phase for movement from that left turn lane is needed The following guidelines applicable to intersections having separate left turn lane
70. ions the performance index is a user specified balance between delav and stops Phasing and cycle length are not optimized in most versions Basic inputs include cycle length phasing performance index weights lost time link lengths either link travel times or speeds link flows turning movements and saturation flows Basic link outputs include percent saturation total travel travel time delay rate of stops maximum queue lengths offsets and splits Network outputs include similar statistics plus the value of the performance index Flow profile plots are optional TRANSYT 7F uses North American nomenclature on input and output rather than English It also produces a time space plot and estimates of fuel consumption A recent revision optimizes cycle lengths and identifies potential intersection blockages TRANSYT s main advantage is that it uses a fairly realistic flow model without requiring outrageous run times The main disadvantage is the extensive data collection required It has been used extensively and is available in a microcomputer version 92 Sources of Information Detailed information on the previously mentioned programs plus other programs not mentioned can be found in the following sources 1 Developments in Traffic Signal Systems Transportation Research Circular Number 282 July 1984 Handbook of Computer Models for Traffic Operations Analysis Technology Sharing Report FHWA TS 82 214 Federal Highway
71. ips Generally the 12 hour volume between 7 00 a m and 7 00 p m is from 70 to 75 of the 24 hour volume and the peak hour volume is from 10 to 12 of the 24 hour volume Thus if either a 12 or 24 hour count is conducted or known then the peak hour volume can be estimated Further approximately 60 of the traffic volume during the peak hour is in the heavier direction in suburban areas In central areas the approximate percentage in the heavier direction of flow is 55 As an example of the usage of these rel tionships a 12 hour count at an intersection in a suburban setting shows a volume of 700 vehicles Thus the 24 hour volume can be estimated at 1 000 vehicles and the peak hour volume which generally occurs in the afternoon can be estimated at 100 vehicles Finally the two approach volumes can be estimated at 60 vehicles and 40 vehicles It is emphasized that actual traffic counts provide much better timing than counts estimated from these relationships 42 DIRECTIONAL TRAFFIC MOVEMENT INTERSECTION OF ROUTES COUNTY LOCATION DATE Vu Mn WEATHER wi APPROACHING INTERSECTION ON FROM ON FROM ROUTE THE ROUTE THE WEST NORTH SOUTH nouns er run mr rem wr pres vr mem reo Eum RE OE E D SS UE Il woe ENSURE SE ee RO UN RU ER
72. is constructed Closed Network A closed network or grid system contains two or more common intersections 11 sianals in the network should have the same cycle length which is the longest cycle required by any intersection in the network After the cvcle length is selected the timing of each route should be developed separately If necessary adiustments are then made to the offsets or green and yellow times or both to achieve a balance In other words the sum of the offsets plus the green and yellow times taken in sequence around a closed network must be equal to the network cycle length or multiple thereof Manual application of these procedures is difficult and generally not needed by the targeted group for this study therefore the procedures are not described further In practice those responsible for grid systems usually have access to a computer and the timing programs described in the next section of the report However a manual procedure for analyzing a simple closed network is provided in Appendix C This procedure has been reproduced from the course notebook for a signal workshop conducted by the Georgia Institute of Technology 12 SIGNAL TIMING COMPUTER PROGRAMS There are a variety of computer proarams which calculate sianal timing There mav be versions of the same program that run on mainframe mini or microcomputers and the programs may be in the public domain which are free except for processing charges or may be
73. is recommended that each approach be observed for 60 point samples with the field crew moving from approach to approach until all have been studied This procedure can be repeated to obtain an additional 60 point samples on each approach if time permits is recommended that lengths of studies be either 60 90 or 120 point samples Determine Interval Between Samples if a signal is operating in a pretimed or system mode use a 13 second interval for cycle lengths of 45 60 75 90 105 120 135 or 150 seconds For all other cycle lengths in a pretimed or system mode use a l5 second interval between samples For all traffic actuated signals not operating in a system use a l5 second interval Select Observation Point Usually the best location is on the right hand side of the approach in the shoulder or sidewalk area However if the site is hilly other locations may be better Figure B 1 shows possible locations If a vehicle is used it must be positioned so as not to be conspicuous or hazardous to traffic using the intersection Rooftops or buildings offer good locations 4 For traffic signals operating on a fixed cycle length the interval between samples should not be an even divisor of the cycle length This restriction is not important when the cycle length is greater than 150 seconds FIGURE 1 LOCATION OF FIELD OBSERVATION POINTS STOP LINE 2 3 2 lt 215 il 5 pi 2 a wi Oo S
74. j r e gt o z Legend 1 Recommended observation point for Intersection Delay Study midway along length of average maximum stopped queue to be observed 2 2 Preferred observation points for Percent Stopping Study B 6 4 PERCENT STOPPING STUDY 4 1 STUDY OBJECTIVES The objectives of the Percent Stopping Study are to develop an estimate of the percent of vehicles stopping on approaches to signalized intersections and to develop an estimate of total volume on these approaches The volume estimate is used with values derived from the Intersection Delay Study see Section 3 to report delay on a per vehicle basis i 4 2 STUDY REQUIREMENTS Because the Percent Stopping Study will almost always be performed in conjunction with the Intersection Delay Study much of the study design will be accomplished as part of the delay study Hand Counters each percent stopping observer may be equipped with two hand counters The counter is used to register two categories of count stopping and not stopping If such counters are not available the observers simply use tally marks to record the count on the field data sheet Timing Device for Sampling Points 1 per team it is recommended that a small battery powered cassette recorder or other audio device be used to provide an audible cue at each sampling point The tape should start with the word begin to signify the zero point of study Then a cue the word no
75. line of the through band The phases are then constructed at each intersection so that the beginning of a green phase is placed on the construction line at each intersection The top line of the through band is placed parallel to the bottom line If all signals have the same phase length then the through band width is equal to the green plus yellow portion of the cycle If the phase is not the same at all signals the through band width is equal to the shortest green plus yellow period in the system Offsets are determined by measuring the displacement of the beginning of the green interval at individual intersections from the beginning of the green interval at the master station For the example system assume a cycle length of 60 sec a speed of progression of 25 mi h and direction of progression from A Street to R Street a Line A is first constructed with a slope equal to 25 mi h with a 60 sec cycle See Figure 26 b Signal phases are laid out at each intersection with the beginning of green placed on line A top line of the through band is then drawn Since in the example system there is a uniform split of 50 the through band is equal to the green plus yellow period of 30 sec d Assuming A Street to be the master intersection with zero offset the individual intersection offsets are as shown in Figure 26 e It should be noted that although no recoanizable through band exists in the opposite direction oppos
76. local or slave controllers at the individual intersections when to change phases The master controller may simply be one of the intersection controllers which acts as a master and the number of timing plans is dependent on the capabilities of the individual controllers There may be a separate independent master controller located in the field or in some convenient office This independent master can range from a simple electromechanical dial driven by a time clock to a highly 67 sophisticated programmable controller having the capability of scheduling a number of timing plans Traffic patterns however should be constant over time since the timing plans are prescheduled This type of system is relatively simple and has the capability of changing timing plans at one location however the interconnection may be costly especially for systems where intersections are far apart Traffic Adjusted System A traffic adjusted system is characterized by the fact that timing plans are adjusted according to changing traffic conditions by an analog computer receiving volume information from sampling detectors located on the roadway Based on the traffic demand the computer within certain constraints selects the best system cycle length offsets and splits Additional expense is incurred because of the need for detectors Computerized System Computerized systems are characterized by centralized control through a digital computer and two way c
77. located to each of the phases Detector a device which detects the passage or presence of a vehicle with the purpose of advising a controller of the need for a green indication For purposes of this project detectors will be categorized as either small area detectors or large area detectors Small area detectors provide passage point motion or unit detection It is noted that a 6 x 6 foot loop is often used as a 64 10 11 point detector These detectors simply register the passage of a vehicle Large area detectors provide presence or area detection These detectors register the presence of a vehicle in the zone of detection Sampling detectors are placed upstream of the intersection to count the vehicles and provide volume data to the controller or computer which is operating the system Offset the time difference in seconds or percentage of cycle length between the start of the green interval at one intersection and the start of the green indication at another intersection or from another system reference point See Figure 15 Yield point associated with actuated controllers a reference point in the cycle where the controller vields the right of way to an opposing phase It marks the end of the non actuated phase on the major street and establishes the background cycle for coordination Time space diagram a graphical representation of a signa system showing cycles splits offsets and distance relationships o
78. lt in gap may be the same or even exceed the gap selected to retain the green therefore the setting on the passage time dial conceivably could be zero The passage time at high speed intersections defined generally as those having speeds areater than 35 mi h is treated somewhat differ ently Since most high speed intersections are controlled by the Vir ginia Department of Highways and Transportation the two most common types of operations are described in this report The first treatment considers the fact that at high speeds the decision to stop or continue at the onset of a yellow clearance interval becomes a much more critical issue than at slow speeds The area in which this indecision occurs is called the dilemma zone Motorists cauaht outside the dilemma zone or away from the intersection generally reach the decision to stop when a yellow indication is observed Motorists inside the dilemma zone or toward the intersection generally decide to proceed through the intersection The boundaries of the dilemma zone are given in Table 6 51 Table 5 Built In Gaps for Large Area Detectors Seconds Length of Detector Average Approach Speed mi h ft 5 20 25 3 3 0 5 n 20 1 8 1 4 144 0 9 0 8 0 7 0 6 30 2 3 1 7 1 4 1 1 1 0 0 9 0 8 40 2 7 2 0 1 6 1 4 1 2 1 0 0 9 50 3 2 2 4 1 9 1 6 1 4 1 2 1 1 60 3 6 2 7 2 2 1 8 1 6 1 4 1 2 70 4 1 3 1 2 5 2 0 1 8 1 5 1 4 80 4 5 3 4 2 7 2 3 1 9 1 7 1 5 90 5 0 3 8 3 0 2 5 2 1 1 9 1 7 100
79. n is utilized is as follows 1 Determine the maximum number of vehicles n that can be stored in a single lane between the stop bar and the point detector by dividing the distance in feet between the two by 20 and rounding up 2 Determine the minimum green setting by applying the formula 56 2 1 3 7 Application of this formula for various detector spacings is given in Table 7 3 For pre NEMA controllers the initial interval should be set as the difference between the above minimum green and the passage time interval Table 7 Minimum Green Time versus Point Detector Spacing Distance Between Stop Bar Minimum Green and Detector ft sec 0 40 7 9 41 60 16 0 61 80 12 1 81 100 14 2 101 120 16 3 121 140 18 4 Source Reference 3 If detectors are located at the stop bar there is no finite distance in which a vehicle can be stored without being detected Accordinglv the minimum green conceivably could be set at zero There are practical considerations most related to motorists expectations however which require that a minimum green time of between 4 0 and 7 0 seconds be set For high speed intersections the point detectors are typically Tocated a considerable distance from the intersection to allow a passage time interval setting between 3 0 and 5 0 seconds A minimum green based on the assumed storage of vehicles in that distance results in excess areen being given to that phase when traffic is light and
80. nd the probability of platoon dispersal increases The Manual on Uniform Traffic Control Devices states that Traffic control signals within 0 5 mile of one another along a major route or in a network of interconnecting major routes should be operated in coordination Although this suggests a maximum spacing between signalized intersections of 0 5 mile for effective coordination there are many examples of effective coordination where signals are spaced up to a mile apart particularly where roadside friction is minimal speeds are high and signals are visible for some distance in advance of the intersection Generally it is best to attempt to coordinate intersections if at all possible to maintain traffic flow in platoons The following advantages of providing coordination among signals are listed in the Transportation and Traffic Engineering Handbook 7 1 higher level of traffic service is provided in terms of higher overall speed and reduced number of stops 2 Traffic should flow more smooth v often with an improvement in capacity and decrease in energy consumption 3 Vehicle speeds should be more uniform because there will be no incentive to travel at excessively high speed to reach a signalized intersection before the start of the green interval yet slower drivers will be encouraged to speed up to avoid having to stop for a red light 63 4 There should be fewer accidents because platoons of vehicles will arrive at
81. ng are the steps necessary to obtain the CLV for each phase 18 Characteristics Pedestrians minimal Buses none Approach speeds 25 mi h Control 2 phase pretimed 375 28 ft N 44 ft 65 747 290 Total Passenger Left Volume Cars Trucks Turns Approach vph vph vph 2 Northbound 290 255 35 10 Southbound 375 322 53 12 Eastbound 864 786 78 20 Westbound 747 695 52 25 Figure 5 Example intersection A Source Reference 2 19 Phase 1 North South Movement Northbound Southbound Trucks as PCEs 1 75 35 61 1 75 x 53 Passenger Cars 255 Total 316 Left turn traffic 10 x 316 32 12 x 415 Left turns as PCEs 1 75 x 32 56 1 75 x 50 Through and right turn traffic 90 x 316 284 88 x 415 Total approach PCEs 340 CLV Phase 1 452 PCE hr Phase 2 East West Movement Eastbound Westbound Trucks as PCEs 1 75 x 78 137 1 75 x 52 Passenger Cars 786 Total 923 Left turn traffic 20 x 923 185 25 x 786 Left turns as PCEs 1 75 x 185 324 1 75 x 197 Throuah and right turn traffic 80 x 923 738 75 x 786 CLV Phase 2 738 PCE hr largest of 738 324 345 590 CLV Total 452 738 1 190 PCE hr As a second example consider the intersection shown in Figure 6 Following are the steps necessary to obtain the CLV for each phase 20 93 322 415 50 87 365 452 91 695 786 197 345 590 Approach Northbound Southbound Eastbound Westbound 710 Total Volum
82. nterval were used to develop the information in Table 3 This table has been reproduced in this section for the convenience of the reader For a given approach speed the yellow change interval plus the total phase change interval for various intersection widths are presented The all red interval is the difference between the two given intervals 60 Table 3 Phase Change Intervals Total Clearance Interval Approach Yellow Change Yellow Plus 11 Clearance Speed Interval for Crossing Street Widths ft mi h sec 30 50 70 90 110 20 3 0 4 2 4 9 5 5 6 2 6 9 25 3 0 4 2 4 7 5 3 5 8 6 4 30 3 2 4 3 4 8 5 2 5 7 6 2 35 3 6 4 5 4 9 5 3 5 7 6 1 40 3 9 4 8 5 1 5 5 5 8 6 1 45 4 3 5 1 5 4 5 7 6 0 6 3 50 4 7 5 3 5 6 5 9 6 2 6 4 55 5 0 5 7 5 9 6 2 6 4 6 7 Source Reference 3 Walk and Pedestrian Clearance Pedestrian movements at a signalized intersection are typically accommodated by one of the following methods 1 Pedestrians cross the street with the parallel vehicular green indication with no pedestrian signals 2 Pedestrians cross the street with the parallel vehicular areen indication as instructed by special pedestrian signals 3 Pedestrians cross the street on an exclusive phase when all vehicular traffic is stopped For any of the above methods sufficient time must be provided for pedestrians to enter the intersection called the walk interval and to safely cross the street called the pedestrian clearance interval
83. ntroller operates according to a predetermined schedule that is it has a fixed cycle length which is subdivided into discrete preset phases to accommodate required individual traffic movements This type of equipment is best suited when traffic patterns and volumes are predictable and do not vary significantly There is some flexibility in timing as most controllers allow for at least three independent timing plans which are generally based on time of day or day of week variations in the traffic patterns Definitions The following definitions are applicable to timing pretimed signals See Figure 1 1 Timing plan a unique combination of cycle length and split 2 Cycle the time required for one complete sequence of signal indications 3 Phase that part of a signal cycle allocated to any combination of one or more traffic movements simultaneously receiving the right of way during one or more intervals 4 Interval a discrete portion of the signal cycle during which the signal indications remain unchanged 5 Split the percentage of a cycle length allocated to each of the phases poem Cycle meses Phase Main St Second St Red Green Yellow Phase 2 Interval Interval Interval Figure 1 Timing sequence for simple two phase controller Objective The major objective of signal timing is to assign the right of way to alternate traffic movements so that all vehicles are accommodated with a minimum amount of
84. o max switch should be activated to ensure service to a phase if the detectors are broken It may be beneficial during periods of low volume to have the controller resting in green on the major street In this case the minimum vehicle recall switch on the main line phase is activated Obiective The major objective of signal timing is to assign the right of wav to alternate traffic movements so that all vehicles are accommodated with a minimum amount of delay to any single group Actuated contro is responsive within certain limitations to traffic demand and thus can provide very efficient operation at an intersection Unlike pretimed control cycles and phases vary in timing and sequence Thus timing actuated controllers involves the understanding of and setting of the preset intervals or timing parameters alluded to in the previous discussion on types of controllers These parameters must be set for each phase in the cvcle Timing Procedures As indicated earlier the essential part of timing actuated intersections is the setting of values for the timing parameters Several other steps are necessary however and following is a list of the recommended procedures The basic concepts and if applicable suggested settings are described in the remainder of this section l Collect necessarv information at the intersection 2 Determine number of phases needed 3 Determine values for timing parameters 4 Verify or adiust timing after
85. of the diagram This aid was developed by Professor Clyde E Lee at the University of Texas at Austin in the 1960s for constructing time space diagrams With the aid folded the shading along the crease indicates artery green time by white and artery red time by black The center of each of these intervals is marked on the aid Place the aid folded at 50 adjacent to the vertical time line at intersection A with the beginning of artery green white on aid at the origin Mark heavy bars on the diagram along the vertical time line to show artery reds black on aid being careful to start and end these bars accurately Also mark the center of the first green interval and draw a horizontal line on the diagram to serve as a reference time at the other intersections NOTE The aid may be used at the 5 000 ft intersection to locate the horizontal reference time line accurately on the diagram The successive green and red signal indications that will be viewed by drivers on the artery as they approach intersection A are thus shown on the vertical time axis of the diagram Next fold the aid to the percentage of artery green at intersection B and align the crease beside the vertical time line at this intersection location Adjust the aid vertically to center the artery red indication on the horizontal time reference line and notice that the beginning of artery green is offset for a speed of progression of approximately 26 mi h and that most of the
86. of volume density features offers particular advantages on high speed approaches where detectors are located several hundred feet from the intersection Specific characteristics are as follows 1 Detectors are located on all approaches to the intersection 2 Each phase receives a minimum green which can be extended as additional vehicles queue up at the red indication 3 Once the minimum or extended minimum green is reached the green is maintained by additional calls until a preset maximum is reached or a preset gap in traffic occurs In the case cf volume density control the preset gap can be reduced after a period of time so that the areen is terminated at the occurrence 0f a smaller gap than necessary at first 38 4 yellow change and all red clearance intervals are preset for each phase Phase Control Functions Each phase on an actuated controller has several switches which control functions or modes of operation for that phase Although these functions are not specifically related to timing it is important to be aware of their operation Following is a brief description of the modes Lock Detector When a vehicle actuates a detector on a phase which is set in the lock detector mode that call is locked in the memory of the controller until such time as that phase is serviced or receives a green indication Small area or point detectors require that the controller be set in this mode Non lock Detector A pha
87. ommunication between the computer and the individual intersection controllers and detectors The most common control approach is to let the computer handle all of the timing functions based on traffic demand and use the intersection controllers to merely change the signal display lamps These systems offer practically unlimited flexibility in implementing signal timing plans They also offer additional advantages including the ability to monitor system performance and to detect system malfunction The disadvantages of computerized systems are the high costs of installation and maintenance and the complexity which generally requires additional personnel expertise Types of Proaression There are four general ways in which continuous flow or progression through an arterial signal system is achieved These are discussed below Simultaneous Progression If simultaneous progression is used all signals along the route which are in the system operate with the same cycle length and display the green indication at the same time All traffic moves at one time and a short time later all traffic stops at the nearest signalized intersection to allow cross street traffic to move This type of 68 y progression is typically used in downtown areas where intersections are close together 300 to 500 feet and the spacing is reasonably uniform Offsets at all intersections are zero See Figure 16 Alternate Progression With alternate progression
88. on Only 11 of the local jurisdictional systems use time based coordination This is explained by the fact that the Department is continually upgrading and expanding its signal systems Due primarily to budget constraints cities and towns cannot do this on a routine basis Auxiliary stand alone equipment is generally being phased out through modernization programs as the functions performed by this equipment are built into the new replacement controllers Auxiliary equipment that is still commonly found includes minor movement controllers and coordination units Inductive loop detectors are the most commonly used type For those respondents reporting actual numbers of detectors it was found that there are approximately 5 700 loops or 782 of the total number of detectors The next most common at 1 200 and 17 are magnetic detectors There are only a few magnetometers radar and pressure detectors Computers are available to a limited extent at the local level Seventeen of the responding jurisdictions have microcomputers whereas another 10 have access to a mini or mainframe computer Only 4 of the Department s construction districts reported the availability of a microcomputer however the other 5 should be receiving micros shortly Thus the use of signal timing computer programs is feasible for many of the agencies maintaining signals in Virginia TIMING FOR PRETIMED SIGNALS AT ISOLATED INTERSECTIONS Background A pretimed co
89. oudh traffic if intersection geometrics promote hazardous conditions or if there are access management problems It is emphasized that the above are guidelines and should be coup ed with engineering iudgement More detailed information on these guidelines plus guidelines for using protected permissive phasing can be found in the above referenced report gt 15 Calculate Passenger Car Equivalents The timing procedures described later require that volumes be known in terms of passenger car equivalents per hour The use of PCEs accounts for the negative impacts of trucks buses and turning vehicles on the traffic handling capability of an intersection Trucks and buses not only occupy more space than an automobile but they also require more start up time due to their acceleration characteristics Trucks havina 6 or more tires and intercity buses should be considered the equivalent of 1 75 passenger cars Local buses stopping in the vicinity of the intersection have even greater negative impacts than do intercitv buses and should be estimated to be the equivalent of 5 0 passenger cars Turning vehicles also have an adverse impact on intersection operation Left turning vehicles which must yield to oncoming vehicles should be considered the equivalent of 1 75 passenger cars and right turning vehicles yielding to pedestrians on the cross street should be estimated at 1 25 passenger cars 3f the number of right turns is more than 10
90. pped Delay the total amount of stopped time in vehicle seconds for all vehicles using an intersection approach during a given period of time Stopped Delay Per Vehicle stopped delay divided by the total number of vehicles passing through the intersection approach during a period of time in vehicle seconds per vehicle Stopping a vehicle which comes to a stop one or more times on the intersection approach B 4 3 INTERSECTION DELAY STUDY 3 1 STUDY OBJECTIVES The principal objective of the Intersection Delay Study is to collect data on the approach to a signalized intersection such that an accurate estimate of approach delay per vehicle and stopped delay per vehicle can be made The Percent Stopping Study see Section 4 for description must be taken simultaneously with the delay study in order to calculate these two measures of performance on a per vehicle basis 3 2 STUDY REQUIREMENTS step by step approach should be followed in the design of an Intersection Delay Study The following elements must be considered Select Time Period To Be Studied for most applications a peak traffic period and an off peak period should be studied to give a balanced view of intersection operation Select Length of Study Period a minimum of 60 point samples should be taken for each study This represents a 15 or 13 minute period depending on the interval between samples used If an entire intersection is to be studied it
91. pplied procedures for timing the various types of signals The Technical Report provides the user with the theory and logic underlying the summarized procedures in the Field Manual and should be reviewed to obtain a thorough understanding of timing Also some of the definitions and timing procedures are applicable to more than one category of signals In these cases the information is often duplicated for the convenience of the user INVENTORY OF EQUIPMENT A survey was conducted to determine the types of control equipment in use in the state of Virginia The questionnaire in Appendix A was sent to 65 cities and towns the 2 counties that maintain signals and the 9 construction districts of the Virginia Department of Highways and Transportation Responses were received from 26 cities 16 towns 2 counties and 9 construction districts Following is a summary of the survey results Manufacturers Table 1 shows the responding jurisdictions and the manufacturers of the signal controllers that each has The most commonly used control lers in Virginia were manufactured by Crouse Hinds Automatic Signal or Eagle It is interesting to note that the Department utilizes the largest variety of manufacturers partly because of the large number it maintains and partly because it continually purchases equipment on a low bid basis Isolated Intersections Based on the responses received essentially all of the Department s signalized intersections
92. r If Figure 7 is entered on the horizontal axis at 1 190 an optimum cycle of 50 seconds can be read from the vertical axis across from the 2 phase curve Similarly the 1 248 PCEs hr at the 3 phase intersection in example B has an optimum cycle of 75 seconds 24 1400 1200 1000 800 CEE REE L ttt EEN LI 600 Sum of Critical Lane Volumes pce hr 400 200 LL LLLA LL is i oO e N e co Nel d N 335 2 91242 unututw 25 Optimum cycle length for pretimed control Source Figure 7 Reference 2 It is noted that in practice cycle lengths should be no less than 40 seconds and no greater than 120 seconds In recent years the tendency has been to use longer cycles even more than 120 seconds Timing above and below these limits will cause excessive delay and motorists impa tience If a cycle greater than 120 seconds is required consideration should be given to alternative solutions such as intersection modifica tions Calculate Cycle Splits Cycle splits expressed in seconds for each phase can be calculated by the following equation from Webster s Method GHA C L 1 3 Y where for the phase being considered green time in seconds A phase change or clearance interval in seconds y ratio of the actual volume to the saturation volume for the critical approach for the phase Y total of the ratios of the actual
93. raffic is alternately directed to stop and permitted to proceed Signals are most commonly used at street intersections to control the assignment of vehicular or pedestrian right of way thus they exert a significant influence on traffic flow Signals that are warranted and are properly designed installed and operated provide for the orderly efficient movement of traffic They also increase the traffic handling capability of the intersection and reduce the frequency of certain types of accidents One of the most important elements of signal operation is signal timing which can be defined as the proper assignment of time to the various vehicular or pedestrian movements at a particular intersection As compared to a correctly timed signal a signal timed improperly can result in increases in delay in gasoline consumption and air pollution and in certain types of accidents Signal timing has received a great deal of attention in recent years as the importance of utilizing the existing transportation system in the most efficient manner has been recognized There are many signal timing procedures and strategies and they vary according to the type and capability of the controller and the traffic requirements at the intersection Pretimed and vehicle actuated controllers are timed differently as are the signals located at isolated intersections at intersections along an arterial and at intersections in a system network Further the timing proced
94. rance intervals over the course of a cycle as the number of phases increases The number of phases required at an intersection is most often a left turn issue As the volumes of left turn and opposing traffic increase it becomes more difficult for the traffic turning left to find adequate gaps A separate left turn lane can alleviate the problem to some degree by providing storage for vehicles awaiting an adequate aap however at a certain point a separate phase for movement from that left turn lane is needed The following guidelines applicable to intersections having separate left turn lanes may be used when considering the addition of separate left turn phases These are contained in a recent report entitled Guidelines for Exclusive Permissive Left Turn Signal Phasing by B Cottrell 1 1 Volumes consider left turn phasing on an approach when the product of the left turn volume and opposing volume divided by the number of lanes during the peak hour exceeds 50 000 provided that the left turn volume is greater than two vehicles per cvcle on average 2 Delay consider left turn phasing if a left turn delay of 2 9 vehicle hours or more occurs in the peak hour provided that the left turn volume is greater than two vehicles per cycle on average Also the average delay per left turning vehicle must be at least 35 sec See Appendix B for a procedure for determining intersection delay 3 Accident experience consider left turn
95. report of the research project is in three volumes Volume No FHWA No Short Title 1 FHWA RD 76 135 Technical Report 2 FHWA RD 76 136 Data Summaries 3 FHWA RD 76 137 User s Manual Source Procedure for Estimating Highway User Costs Fuel Consumption and Air Pollution U S DOT FHWA Office of Traffic Operations Washington D C May 1980 1 INTRODUCTION 1 1 MEASURES OF PERFORMANCE In traffic engineering work it often becomes necessary to report on the efficiency of operation of intersections controlled by traffic signals The 1965 Highway Capacity Manual describes intersection performance in terms of load factor and ratios of volume to service volume More direct and practical measures of intersection performance are vehicle delay and the percentage of vehicles having to stop There are two fundamental reasons why delay and stops are good measures of intersection performance motorists are keenly aware of and sensitive to the number of stops they are forced to make and to the length of time they are delayed and measures of stops and delay can readily be applied to estimates of road user costs fuel consumption and environmental impacts of traffic flow 1 2 SUMMARY OF THE METHODS This manual contains complete instructions for the application of two methods which lead to estimates of vehicle delay and stops on approaches to signalized intersections It is recommended that the two methods be applied simultaneously in the field
96. roach traffic should be categorized into the number of vehicles turning left going straight through and turning right It is also necessary to count and record the number of buses and large trucks per hour on each approach Finally the average speed of traffic approaching the intersection on each leq should he obtained 41 The traffic and pedestrian data are needed for the peak flow condition at the intersection Typicallv peak flow occurs during the afternoon rush period however side street peak flow may occur at another time during the day Likewise peak flow at the entrance to a shopping center may occur around 9 00 p m Accordingly it is important to obtain the data over a period of time which will definitely include the peak flow condition A tvpical data collection form was provided previously in Figure 2 It is noted that the volumes are tabulated by one half hour intervals during the norma morning and afternoon rush hours This enables a more accurate determination of peak hour statistics than would be possible with one hour summaries Volume counts by 15 minute intervals would be the most accurate Figures 3 and 4 showed other common forms used to summarize the data for 3 legged and 4 legged intersections respectively These figures have heen reproduced in this section of the report for the convenience of the reader Although undesirable it is possible to derive an estimate of the peak hour volume based on general relationsh
97. rvey which had the objective of determining the types of signal equipment used in Virginia 4 30 85 SI CONVERSION FACTORS To Convert To Multiply From Length in 2 54 in mn 0 025 4 n 0 304 8 yd m 0 914 4 mi 609 344 2 2 in ee 6 451 600 E 00 semen 9 290 304 E 02 yd 8 361 274 E 01 mi Hectares 2 589 988 02 acre a Hectares 4 046 856 01 Volume 2 2 2 957 353 E 05 er 4 731 765 E 04 6 mes 9 463 529 E 04 ER eerie aera ea emma 3 785 412 03 inj SS ee 1 638 706 E 05 ft SS ee ee 2 831 685 E 02 yd M 7 645 549 01 NOTE 1m 1 000 L Volume per Unit Time era al uj PREISER 4 719 474 E 04 ft s 2 831 685 02 min 2 731 177 E 07 min 1 274 258 02 gal min 6 309 020 05 Mass oz
98. s 305 174 842 1 321 Find Critical Lane Volumes A critical lane volume CLV is the highest lane volume in vehicles per hour vph for a particular phase In this step the CLV for al phases must be determined and then summed over the entire intersection If enough green time is provided to handle the lane having the highest volume during a phase then there automatically is sufficient green to accommodate other lanes of traffic moving during that phase The following general rules apply to calculating the CLV l CLVs are calculated in PCEs 2 Right turn and left turn movements are considered part of the through movement unless there are exclusive turn lanes 17 3 Exclusive left turn and right turn lanes without separate phasing should be assigned the appropriate number of PCEs as determined by the 1 75 factor for opposing traffic to left turns or the 1 25 factor when right turns are more than 10 or pedestrian flow is significant The turning volumes should then be compared directly with the through volumes to determine the CLV 4 If the left turn movement is protected from conflict with separate phasing the adjustment factor of 1 75 is not applied 5 When 2 approach lanes handle through traffic it should be assumed that the critical lane carries 55 of the volume Likewise for 3 approach lanes the critical lane is assumed to carry 37 of the volume As an example consider the intersection shown in Figure 5 Followi
99. s may be used when considering the addition of separate left turn phases These are contained in a recent report entitled Guidelines for Exclusive Permissive Left Turn Signa Phasing by B H Cottrell Jr 1 1 Volumes consider left turn phasing on an approach when the product of the left turn volume and opposing volume divided bv the number of lanes during the peak hour exceeds 50 000 pro vided that the left turn volume is greater than two vehicles per cvcle on average Delav consider left turn phasing if a left turn delav of 2 0 vehicle hours or more occurs in the peak hour provided that the left turn volume is greater than two vehicles per cycle on average Also the average delav per left turning vehicle must be at least 35 sec See Appendix B for a procedure for determining intersection delay Accident experience consider left turn phasing if the critical number and resulting rate of left turn accidents have been exceeded For one approach the critical number is five left turn accidents in one year The accident rate as defined by the annual number of left turn accidents per 100 million left turn plus opposing vehicles must exceed the critical rate determined by the equation Rc 32 6 1 6454 32 6 M 0 5 M where M is the annual left turn plus opposing volume in 100 million vehicles Site conditions consider left turn phasing if there is inadequate sight distance if there are three or more lanes of opposing thr
100. se set in the non lock detector mode sends a call to the controller onlv if a vehicle is present in the detection zone Once the vehicle moves out of the zone the call for service is cancelled Large area or presence detectors require this settina This mode of operation is appropriate for locations where right turn on red occurs and for left turn phases with exclusive permissive control Non actuated A phase set in the non actuated mode automatically operates under semi actuated control with that phase controlling the major street or non actuated traffic flow Recall When the recall switch on a phase is on the controller automatically returns to that phase during each cycle If all recall switches are activated the controller automatically cycles through all phases Jn this case the controller operates in a pretimed manner and all advantages of actuated control are lost no recall switches are activated the controller stays in the last serviced phase indefinitely until a call is received from another phase There are several variations of this mode If minimum vehicle recall is set when the detectors are functioning the controller 39 automatically returns to the phase to service the minimum green and then operates based on demand A vehicle recall to max setting causes the phase s maximum green interval to time out Finally a pedestrian recall setting causes the pedestrian intervals to time out The vehicle recall t
101. sed in second group of 30 samples FIGURE B 3 PERCENT STOPPING STUDY FIELD DATA SHEET PERCENT STOPPING STUDY Intersection 7105077 Sha 2221 Sf Study Traffic on 22 Zo City and State son Az Agency City of tesan Engineering Civ Day Date 727 2 976 study Period 247 252 observer l Burke Traffic Approaching From N Weather 707 N E S W If more than one person is studying same approach explain division of responsibilities STOPPING NOT STOPPING ML IF TALLY MARK IS USED THL OENQTES A COUNT 5 TOTAL STOPPING ZO TOTAL NOT STOPPING 223 COMMENTS FIGURE B 4 DATA REDUCTION FORM DATA REDUCTION FORM INTERSECTION DELAY AND PERCENT STOPPING STUDIES intersection TUCSON BLVO 22NO 57 ciy s UC SON ARIZONA Study Approach On TUCSON LVO Traffic Prom N N ma tim MOM AUG 2 976 1340 1353 O OO FERCENT STOPPING STUDY 4 Total no of vehicles stopping 44 Total no of vehicles not stopping 444 Total volume i ii iv Observed Percent stopping i iij x 100 v Actual Percent of Vehicles Stopping iv x 0 96 CORRECTION PROCEDURE FOR MISSED SAMPLES IM DELAY STUDY Total ao of point samples taken in field during i0 sample period 30 a Sum of point sample values for 30 sample period on field data sheet Value of each missing sample c round to n
102. t discussed Minimum Green Actuated Phase The minimum green interval for an actuated phase is set to allow vehicles stopped between the detector and the intersection to get started and move into the intersection If small area or point detectors are being used there is a finite distance between the detector and the intersection in which vehicles can be stored while awaiting a green indication When the green is received a minimum amount of green time is needed to ensure that these stored vehicles can start up and move into the intersection in case there are no further actuations to initiate timing of the passage time interval Studies have indicated that for a single line of vehicles the time in seconds needed to accomplish this can be estimated by the formula 2 1 n 3 7 where n is the number of vehicles Assuming the average length of a vehicle is 20 feet then the number of vehicles can be estimated as the distance between the intersection and the detector divided by 20 feet The minimum green timing parameter is shown schematically in Figures 11 and 12 It is important to note from Figure 12 that for pre NEMA controllers the minimum green is the sum of a setting called initial interval plus the vehicle passage time interval In this case the minimum green is calculated as described above and the initial interval is set by subtracting the vehicle interval In summary the procedure for determining minimum areen when point detectio
103. tant to note that due to the wide variety of hardware components it is not feasible to relate timing parameters to specific dial settings Therefore the instructions for the equipment being utilized must be reviewed closely and related to the timing parameters developed Generally cycle lengths and phase parameters are set on the controllers while offsets and force offs are set on coordinating units 74 Data Collection Depending on the type of equipment being used the data requirements discussed previously for pretimed and actuated signals are also applicable to systems A plot of 15 minute or hourly volumes by direction on the major arterial is a useful tool in setting system timing A graph of this nature allows an easily visualized determination of when cycle lengths and offsets should be changed and if one way or two way progression is acceptable Threshold volumes for changing the cycle length and offsets can also be selected directly from the graph Arterial Systems It is feasible to manually develop timing plans for simple arterial systems Two categories of arterial systems can be identified for purposes of timing those with uniform block spacing and those with nonuniform block spacing Following are procedures for these categories The procedures have been excerpted from the Institute of Transportation Engineer s Transportation and Traffic Engineering Handbook dated 1976 10 and from the University of Texas Center for Tr
104. ted Signal Control Traffic Control Division Automatic Signal LFE Corporation May 1984 Traffic Control Devices Handbook U S Department of Transportation Federal Highway Administration 1983 Transportation and Traffic Engineering Handbook 2nd ed Institute of Transportation Engineers 1982 Traffic Control Systems Handbook Implementation Package 76 10 U S Department of Transportation Federal Highway Administration June 1976 Signal System Timing excerpt from a course notebook The Traffic Institute Northwestern University Evanston Illinois Transportation and Traffic Engineering Handbook Institute of Traffic Engineers 1976 Machemehl Randy B and Clyde E Lee Adding Signals to Coordinated Traffic Signal Systems Research Report Number 260 1F Center for Transportation Research Bureau of Engineering Research The University of Texas at Austin August 1983 Manual Calculations for Network Coordination excerpt from a course notebook Georgia Institute of Technology Atlanta Georgia Developments in Traffic Signal Systems Transportation Research Circular Number 282 Transportation Research Board July 1984 97 APPENDIX A INVENTORY OF SIGNAL EQUIPMENT IN VIRGINIA A 1 INVENTORY OF SIGNAL EQUIPMENT IN VIRGINIA The Virginia Highway and Transportation Research Council of the Department of Highways and Transportation has prepared this questionnaire to obtain an inventory of signal equipment being
105. the 17 microcomputers are IBM Conclusions Based on the results of the questionnaire survey regarding tvpes of signals utilized in the state the following general conclusions can be made 1 Controllers manufactured Crouse Hinds now called Traffic Control Technologies Automatic Signal and Eagle are the most common in Virginia This is the same finding reported in an inventory obtained in 1976 The Department maintains only 4 pretimed signals at isolated intersections the remainder are actuated On the other hand approximately 17 of the signals at isolated intersections reported by local jurisdictions are pretimed Old pretimed equipment is quite common in the small cities and towns Therefore it is still important to discuss timing procedures for pretimed signals The Department maintains 46 signal systems whereas 44 of the 67 local jurisdictions maintain 82 systems 11 of the Department s systems are arterial systems whereas 63 of the local systems are arterial systems The remaining 19 are grid systems Over 1 100 intersections are known to be in a system The majority of the local jurisdictional intersections operate pretimed whereas the majority of the Department s intersections in a system operate semi actuated This is explained by the fact that the 19 grid systems reported by local jurisdictions contain predominantly pretimed intersections Of the Department s 46 systems 26 use the new time based coordinati
106. the intersection or proceed through the intersection prior to commencement of the green interval on the cross street The following equation is used to calculate the phase change interval cP t UL P 5 where CP change period in seconds t perception reaction time usually 1 0 second V approach speed in feet second typically the 85th percentile speed or prevailing speed limit a deceleration rate in feet second usually 10 feet second W width of intersection in feet L length of vehicle in feet usually 20 feet and percent of grade divided by 100 with upgrade being positive and downgrade being negative It is important that motorists have a reasonable expectation of the length of the yellow interval therefore the yellow interval should be set in the range of from 3 0 to 5 0 seconds Within these limits the yellow interval is often set according to the time it takes to decelerate to a stop that is the first two terms in the above equation Yellow intervals that are longer than necessary decrease capacity and encourage motorists to try to beat the light 31 The time needed to clear the intersection as calculated by the last term in the above equation should be included in an all red interval where all approaches receive a red indication Required stopping time above 5 0 seconds should also be included in the all red interval Exclusive turn phases do not typically have an all red interval Normally a thro
107. the maximum green it is important to be aware of how the controller is timing when field checks are being made Finally it should be noted that some controllers are capable of providing two maximum green intervals per phase A time clock or other external control selects the interval to be used The timing would be determined from two sets of volumes and pedestrian counts An example would be the use of a longer maximum green during peak hours than during the remainder of the day Yellow Change and Red Clearance The purpose of the phase change or clearance interval which consists of the yellow interval and possibly an all red interval is to advise motorists of an impending change in the assignment of right of way that is the commencement of a red interval on their approach Upon commencement of the change interval a motorist should have sufficient time to either stop his vehicle or clear the intersection At a given approach speed a certain amount of time is needed to decelerate to a safe stop at the intersection or proceed through the intersection prior to commencement of the green interval on the cross street The previously presented equation 5 is used to calculate the phase change interval V W L 7 where CP change period in seconds ct u perception reaction time usually 1 second 59 V approach speed in feet second typically the 85th percentile speed or prevailing speed limit
108. the storage space is not fully utilized In this case a volume density controller is frequently used In order to utilize the volume density function an additional timing parameter called seconds per actuation needs to be set Some NEMA contro lers also have a parameter called maximum added initial In operation a minimum green time based on one vehicle is set that is 2 1 seconds plus 3 7 seconds or 5 8 seconds Fach additional vehicle approaching the intersection during the nongreen time will actuate the detector and increase the minimum green by the preset seconds per actuation until such time as the maximum added initia green time is reached This operation is depicted schematically in the upper portion of Figure 14 In theorv the seconds per actuation should be set at 2 1 seconds and the maximum added initial should be set to accommodate the maximum storage in a single lane as given by the orevicusly 57 described formula 2 1 n 3 7 This procedure is satisfactory for a single lane approach however in the case of a multi lane approach the seconds per actuation should be set at 1 0 second Again volume density settings should be based on field observations Further pre NEMA controllers may have slightly different ways to account for additional vehicles approaching the intersection therefore it is most important to review the instructions for the specific controller being retimed Minimum Green Non actuated Phase The
109. their computation This volume count will normally be obtained by using the Percent Stopping Study In presenting results an explicit identification of the delay type is essential and the above mentioned terms rather than the vague term delay should be used INTERSECTION DELAY STUDY POINT SAMPLE STOPPED DELAY METHOD Intersection Study Traffic On City and State Agency Day Date Study Period Observer Traffic Approaching From Weather N S E W If more than one person is studying same approach explain division of responsibilities INTERVAL BETWEEN SAMPLES SECS OBSERVED TOTAL ALL SAMPLES DENOTES 30 SAMPLE COMMENTS Ln QA hnc a b C A Unnn hu C C C En Er PE EE SSCS B 13 PERCENT STOPPING STUDY Intersection Study Traffic On City and State Agency Day Date Study Period Traffic Approaching From Weather N E S W If more than one person is studying same approach explain division of responsibilities STOPPING NOT STOPPING TALLY MARK IS USED TL OENQTES A COUNT OF 5 TOTAL STOPPING o TOTAL NOT STOPPING __ COMMENTS Intersection Study Approach On Day Date Time DATA REDUCTION FORM INTERSECTION DELAY AND PERCENT STOPPING STUDIES PERCENT STOPPING STUDY i ii iii iv v Total no of vehicl
110. to operate at force off or pretimed conditions Also a desired speed of progression and the tolerable variations from this speed must be specified The character of the arterial and its surroundings will guide the decision concerning reasonable speeds In the case of two directional flow equal opportunity for progression should be given to each direction Specifically the 77 objective is to have the same speed of progression and band width in each direction such is the case in the off peak hours when the directional split is about the same A general graphical solution for determining the timing plan for off peak signal timing was developed by James H Kell Symmetry in the slope and width of the through band on the time space diagram is attained by centering either the red or the green arterial signal interval on a reference point such that the beginning of artery green will be offset properlv for a speed of progression within the tolerable range The procedure for constructing a time space diagram for an off peak timing plan by Kell s Method is illustrated in the following steps for the series of intersections spaced as shown in Figure 20 For this example the required cycle length is 80 seconds and the percentage of cycle time that will be allocated to artery green is given at the top of the diagram The tolerance range for progression speed is from 25 to 30 mi h The yellow phase change interval is included in the artery green
111. twork 0 25 20 45 0 o A 0 600 20 offset 20 start of gr at B 2 25 green at 8 45 end of gr at B 30 offset BC ul k en start of gr at C 0 50 at 225 20 45 0 25 The notations at each intersection are called designators first number is the offset from the previous intersection the second is the time at the end of the green If any number exceeds a cycle length C is subtracted from it to keep the numbers small for example at C the start of green is at 75 seconds as measured from start of green at A however 75 50 25 is used at C as the first designator This problem ind cated that we can have our desired speed of 20 mph 30 fps provided we are satisfied to have a cycle length of 33 or 50 or 100 seconds Suppose however that it is necessary to use a 70 second cycle at these intersections because of capacity requirements or because these streets must coordinate with other intersections operating at a 70 second cycle In this case it is necessary to adjust the offsets in order that the network will still balance this adjustment will in turn change the speed of progression C 70 seconds cycle split still is 50 50 desired speed still is 30 fps G 35 R 35 secs Calculate offsets desired they are the same as before because speed desired has not changed 0 20 0 20 off 0 30 20 C BC 35 0 20 DEREN D CD 430 off 55 30 85 90 30 65 2
112. ugh movement phase follows the exclusive turn movement therefore motorists receiving the green directly face straggling left turners and can safely yield the right of way An all red interval may be needed however at a high speed intersection or at an intersection with a wide median Equation 5 minus the grade factor coupled with the aforementioned rules regarding the phase change interval have been used to develop the information in Table 3 For a given approach speed the yellow change interval plus the total phase change interval for various intersection widths are presented The all red interval is the difference between the two given intervals It is sometimes the practice to round up the intervals to the nearest 0 5 second As an example of the use of Table 3 again consider the previously described intersections A and B Intersection A 25 mi h approach speed all approaches north south street 28 ft G A 20 sec east west street 44 ft GHA 30 sec Therefore from Table 3 north south st yellow 3 0 sec all red 1 6 sec green 15 4 sec east west st yellow 3 0 sec all red 1 2 sec green 25 8 sec Intersection B 45 mi h approach speed north south 55 mi h approach speed east west north south through 56 ft G A 31 sec east west through 76 ft G A 28 sec east west left lt 16 32 Therefore from Table 3 sec all red 1 5 sec north south through yellow
113. up Software Software packages that are submitted to the center and not fully supported can be copied and distributed to members in the as is condition Limited assistance will be given by the center s staff Software Costs The pricing policy is to charge small fees to help defray the cost of diskettes handling and making copies of documentation Technical Assistance User Group members can write visit or call the Support Center with general questions about the User Group and Support Center or with technical questions regarding hardware and software selection and use Data Base Information Service The Support Center can serve as a liaison between users havina similar problems with or questions about certain programs Contacts with actual users of a program can be very beneficial Notice Effective October 1 1985 the Support Center for the STEAM user group is in transition to as of this writing an undetermined location It is anticipated that the Support Center will be established in its new location by early 1986 In the meantime the aforementioned services provided by the STEAM Support Center can be handled to a limited extent by the Federal Highway Administration s Systems and Software Support Team HT0 23 located in the Office of Traffic Operations 400 7th Street S W Washington D C 20590 The telephone number is 202 426 0411 ACKNOWLEDGEMENTS Many people assisted the author during the course of the study
114. ures range from simple manual techniques to comprehensive techniques applicable to mainframe or minicomputers Techniques are available or are being developed for the microcomputer PURPOSE AND SCOPE Accordingly the main purpose of the study was to compile in a single document recommended procedures for timing the various types of signals Specifically procedures are included for both pretimed and vehicle actuated controllers located at isolated intersections and at intersections in a signal system Simplicity and ease of use are emphasized in the procedures as the targeted users are field technicians and those responsible for maintaining signals in small cities and towns The procedures are based on a synthesis of the pertinent literature Finally brief descriptions of popular computer programs which calculate timing are included A secondary purpose was to survey jurisdictions responsible for signals in Virginia to determine the tvpes of equipment being utilized The survey was conducted through a mail back questionnaire to all cities and towns the two counties that maintain signals and the Department of Highways and Transportation s field offices FORMAT AND USE OF REPORT A separate Field Manual sets forth the recommended procedures in a simplified step by step manner exclusive of detailed background discussion Designed for the most part to stand by itself the Field Manual is intended to provide the user with concise and easily a
115. utilized in Virginia We are interested in both the kinds of equipment and their modes of operation Specifically the inventory has been divided into the categories of controllers at isolated intersections controllers in systems auxiliary equipment and detectors Your assistance in completing the questionnaire would be greatly appreciated Please feel free to add sheets if the space provided is not adequate Thank you in advance for your help Please call me at 804 293 1931 if you have any questions Please return in the enclosed postpaid envelope by April 12 1985 E Geuthp E D Arnold Jr Research Scientist I BACKGROUND INFORMATION 1 Jurisdiction 2 Name of person completing questionnaire telephone no 3 Do you have access to a computer yes no If yes what kind s Mainframe brand Mini brand Micro or personal brand II SIGNAL CONTROLLERS AT ISOLATED INTERSECTIONS Mode Manufacturer Model No No Units 1 Pretimed II SIGNAL CONTROLLERS AT ISOLATED INTERSECTIONS CONT Mode Manufacturer Model No No Units 2 Semi Actuated 3 Fully Actuated 4 Volume Density III SIGNAL CONTROLLERS IN A SYSTEM System No amp Description System No 1 Check all applicable descriptors Type of system ___Grid network Arterial Type of controllers ___Pretimed ___Semi actuated ___Fully actuated ___Volume density Type of interconnect Hard wire How coordinated Street master
116. veloped 2 DEFINITIONS Following are definitions for terms used in the ntersection Delay Study and the Percent Stopping Study Approach Delay The total amount of time in vehicle seconds lost by vehicles due to traffic conditions on the approach to a signalized intersection For an individual vehicle approach delay is the amount of time used to pass through the approach minus the amount of time used by an unimpeded vehicle moving at free flow speed to pass through the approach Approach Delay Per Vehicle approach delay divided by the total number of vehicles passing through the intersection approach during a period of time in vehicle seconds per vehicle Interval Between Samples the time in seconds between each successive point sample of stopped vehicles taken in the Intersection Delay Study Not Stopping a vehicle which proceeds along the intersection approach and enters the intersection without coming to a stop Percent of Vehicles Stopping the proportion of the approach volume expressed as a percent which has stopped one or more times on the intersection approach Point Sample a count of the number of vehicles stopped on the intersection approach or in designated lanes at a given instant in time Sampling Point the instant in time at which a point sample is taken Stopped Time the time in vehicle seconds during which a vehicle is stopped with locked wheels on the intersection approach Sto
117. volume to the saturation volume for the critical approaches C cycle length in seconds L total lost time per cycle in seconds typically 4 0 to 5 0 seconds per phase and 1 lost time for the phase As before the above equation can be modiified if an average lost time of 4 0 seconds and a constant saturation volume is assumed for all phases avi 4N G A 4 4 26 where 6 phase time in seconds as defined before CLV CLV for phase being considered in PCEs hr CLV sum of CLVs per phase in PCEs hr for the intersection C cycle length in seconds and N number of phases Graphical solutions to equation 4 are presented in Figures 8 through 10 for 2 3 and 4 phase control respectively In most cases splits can be obtained directly from the graphs The total of the phase times should equal the known cycle length Again the previously described intersections A and B can be used to exemplify the use of the graphs Intersection A 2 phase C 50 sec CLV 452 PCE hr CLV 738 PCE hr CLV 1 190 PCE hr CLV 452 1 190 0 38 and CLV CLV gt 738 1 190 0 62 Therefore from Figure 8 Entering 0 38 to the 50 sec line G A 4 20 sec Entering 0 62 to the 50 sec line G A 30 sec and Total 50 sec Intersection B 3 phase C 75 sec CLV 238 PCE hr CLV 475 PCE hr CLV 2 535 PCE hr 3 CLV 1 248 PCE hr T 238 1 248 CLV CLV 0 19 CLV CLV
118. w is suggested is given at each sampling point Other Equipment each team member needs a clipboard pencils and enough data sheets for the periods to be studied Each data sheet accommodates 120 point samples A blank sheet is found at the end of this Appendix 5 DATA REDUCTION In the office a data reduction form is filled out for each study period This form an example of which is given as Figure B 4 contains space for reduction of data from both the Intersection Delay Study and the Percent Stopping Appendix Step 1 Step Step Step Step Step Step 7 Study A blank data reduction form is found at the end of this the values for stopping and not stopping are taken from the percent stopping study field data sheets Figure B 3 and entered on lines i and ii of Figure B 4 If two observers were used to perform the Percent Stopping Study the sum of the values from both observers is used Lines i and ii are summed to give a value for total volume line iii Figure B 4 the value for stopping is divided by total volume to give a measure of percent stopping line iv line iv is multiplied by 0 96 see footnote 3 page for comment on this factor to be an estimate of percent of vehicles stopping line v the total volume on line iii is entered on line of the data reduction form so that delay can be computed on a per vehicle basis using data from the field data sheet for the intersection
119. ways and Transportation as well as several local jurisdictions reported that the stand alone equipment is being phased out as quickly as possible Of the stand alone equipment remaining the most common types by far are minor movement controllers and coordination units Detectors The most common type of detector in use in Virginia is the inductive loop detector Six of the Department s construction districts reported actual numbers of detectors and 80 are loop detectors and 20 are magnetic detectors For the districts providing estimated percentages of each kind of detector the average percentages are 65 loops 30 magnetics 2 magnetometers and 3 radar For those loca jurisdictions which reported actual numbers of detectors it was found that 77 of the detectors are loops 13 are magnetics 8 are magnetometers and 2 are pressure sensitive For those 7 jurisdictions reporting a percentage breakdown by type of detector the average percentages are 80 loops and 20 magnetics Availability of Computers Computers are hecoming increasinaly available at the local level Within the Nepartment four of the districts reported the availability of a microcomputer At the local level 61 of the respondents indicated the availability of a computer with 20 of those having access to a mainframe 7 to mini and 63 to a microcomputer The various models of IBM computer are the most common Of particular note is the fact that 10 of
120. xample Gs A B GA DA N Op X N Mos d 5 In order for this example network to be coordinated Os AB Soco pa must be equal to NC where O z offset in seconds of the green at intersection B along street AB B AB 2 This offset is measured from the start of green at the first intersection A of the network AB 8reen plus yellow time in seconds at i tersection B along street AB C length of cycle in seconds N a whole number Since G must be equal to two cycles 2C Ccc it is seen that 0 E Offsets NC 2C C N 2 or 5 5 B AB Onco Pama 6 Example Desired speed 20 mph 30 ps Cycle split 50 50 Required calculate cycle time and offsets 1 Calculate offsets 600 AB 30 20 sec 9 30 sec 0 900 30 0 CD 20 sec 0 DA 30 sec L Offsets 100 sec 2 Determine trial cycle length XL offsets 100 2 N 2 If N23 C 100 Very high N 4 50 N 5 33 3 Very low Try 50 13 Check equation and adjust offsets if necessary 2 offsets 2C NC 100 2 50 4 50 200 200 4 No adjustment is necessary since system is balanced The following line diagram illustrates the offset and green time notations which balance this ne
121. y percent saturation maximum queue percent stops excess fuel and left turn conflicts More are available on request Program documentation is well written and the program is easy to use It has been used extensively and is available for the micro MAXRAND MAXBAND is a band width optimization program that calculates signal settings on arterials and triangular networks The program produces cycle lenaths offsets speeds and phased sequencing to maximize a weighted sum of band widths It can handle as many as 20 signals Basic inputs include the range of cycle lenaths network geometry traffic flows saturation flows left turn patterns queue clearance times and range of speeds Outputs include a data field manual and a solution report that contains cycle time and band widths selected phase sequencing splits offsets and travel times and speed on links The main advantage is the freedom to provide a range for the cvcle time and speed The main disadvantage is its use of band width as its 90 optimization criterion Other disadvantages include the limited experience with field testina and the lack of incorporated bus flows in the optimization It runs only on the mainframe computer PASSER II 80 PASSER II 80 is a band width optimization program that calculates signal timings on linear arterials The program uses a fixed time scan search to produce the cycle length phase sequencing splits offsets and band speed that maximiz

86-R8 - Virginia Department of Transportation

Contents

Download Pdf Manuals

Related Search

Related Contents