Designing a Traffic Signal Timing Plan: Steps and Guidelines

This comprehensive guide covers the essential steps involved in designing a traffic signal timing plan, including determining lane configurations, proposing phase plans, identifying critical volumes, recommending phase plans, and establishing clearance intervals. It also provides insights into aspects like lost time, cycle length, green splits, and displaying greens, offering a detailed walkthrough of the process. The visual aids accompanying the text further enhance understanding and implementation of the timing plan.

• Traffic signal
• Timing plan
• Lane configurations
• Phase plans
• Critical volumes

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1. Traffic Signal Timing Design Part I

2. Steps in Designing a Traffic Signal Timing Plan (1/2) 1. Determine lane configurations and lane volumes 2. Propose Phase Plans (provide diagrams) 3. Critical Volumes for each phase (for each proposed plan) 4. Recommend phase plan 5. Clearance Intervals Slide 2

3. Steps in Designing a Traffic Signal Timing Plan (2/2) 6. Lost Time 7. Cycle length 8. Green Splits 9. Display Greens 10. Provide Final Timing Diagram Repeat as needed for other lane configurations. Slide 3

4. Steps in Designing a Traffic Signal Timing Plan 1. Determine lane configurations and lane volumes 2. Propose Phase Plans (provide diagrams) 3. Critical Volumes for each phase (for each proposed plan) 4. Recommend phase plan 5. Clearance Intervals Slide 4

5. Simple Example (no turns) WB TH 700 SB TH 550 EB TH 450 NB TH 300 Volumes in vph Slide 5

6. Steps in Designing a Traffic Signal Timing Plan 1. Determine lane configurations and lane volumes 2. Propose Phase Plans (provide diagrams) 3. Critical Volumes for each phase (for each proposed plan) 4. Recommend phase plan 5. Clearance Intervals Slide 6

7. Phase Diagram 1 2 Slide 7

8. Steps in Designing a Traffic Signal Timing Plan 1. Determine lane configurations and lane volumes 2. Propose Phase Plans (provide diagrams) 3. Critical Volumes for each phase (for each proposed plan) 4. Recommend phase plan 5. Clearance Intervals Slide 8

9. Critical Lane Volumes WB TH 700 SB TH 550 1 2 V1= max{700,450} = 700 V2= max{550,300} = 550 EB TH 450 NB TH 300 Slide 9

10. Steps in Designing a Traffic Signal Timing Plan 1. Determine lane configurations and lane volumes 2. Propose Phase Plans (provide diagrams) 3. Critical Volumes for each phase (for each proposed plan) 4. Recommend phase plan 5. Clearance Intervals Slide 10

11. Steps in Designing a Traffic Signal Timing Plan 1. Determine lane configurations and lane volumes 2. Propose Phase Plans (provide diagrams) 3. Critical Volumes for each phase (for each proposed plan) 4. Recommend phase plan 5. Clearance Intervals Slide 11

12. Clearance Interval min = tr + [(W+L)/u0] + [u0 /(2a)] L is vehicle length (ft or m) u0 is approach speed of vehicles (f/s or m/s) = tr is driver s reaction time (sec) = a is deceleration rate (ft/s2 or m/s2) = 10 fps2 W is road width to be cleared (ft or m) = ft Slide 12

13. Length of All-red versus Yellow = 4.2 seconds Yellow = 3.5 seconds All Red = 0.7 seconds Notes Typical values for yellow 3 to 4 seconds; use judgment remaining clearance interval time is all red Slide 13

14. Steps in Designing a Traffic Signal Timing Plan 6. Lost Time 7. Cycle length 8. Green Splits 9. Display Greens 10. Provide Final Timing Diagram Repeat as needed for other lane configurations. Slide 14

15. Lost Time L = l1 + l2 assume start and end loss = 2 sec per phase (make assumption if not given in problem) L = 2 + 0.7+ 2 + 0.7 = 5.4 seconds Slide 15

16. Steps in Designing a Traffic Signal Timing Plan 6. Lost Time 7. Cycle length 8. Green Splits 9. Display Greens 10. Provide Final Timing Diagram Repeat as needed for other lane configurations. Slide 16

17. Websters Formula for Optimum Cycle Length Co = 1.5 L + 5 1- yi Co is the optimum cycle length (sec) L is the total lost time including all-red (sec) yi is the critical volume to saturation flow for phase i Slide 17

18. Websters Formula for Optimum Cycle Length Co = 1.5 L + 5 1- yi Notes as L gets larger Co gets larger as volumes get larger Co gets larger Slide 18

19. Websters Formula for Optimum Cycle Length 1.5 L + 5 1.5*5.4 + 5 Co = = = 1- yi 1-[(700/1900)+(550/1900)] = 38.5 sec 40 sec Notes Cycle is typically rounded up to nearest 5 seconds Slide 19

20. Steps in Designing a Traffic Signal Timing Plan 6. Lost Time 7. Cycle length 8. Green Splits 9. Display Greens 10. Provide Final Timing Diagram Repeat as needed for other lane configurations. Slide 20

21. Allocating Green Time gT = C - L = gi = gT (yi / Y) Y = yi Slide 21

22. Steps in Designing a Traffic Signal Timing Plan 6. Lost Time 7. Cycle length 8. Green Splits 9. Display Greens 10. Provide Final Timing Diagram Repeat as needed for other lane configurations. Slide 22

23. Display Green (as opposed to effective green) Gi = gi + li - i G1 = 19.4 + (2+0.7) - (3.5 +0.7) = 17.9 seconds G2 = 15.2 + 2.7 - 4.2 = 13.7 seconds Note the AR is added and then subtracted Slide 23

24. Steps in Designing a Traffic Signal Timing Plan 6. Lost Time 7. Cycle length 8. Green Splits 9. Display Greens 10. Provide Final Timing Diagram Repeat as needed for other lane configurations. Slide 24

25. Timing Diagram Slide 25

26. Reality and Complications Multiples lanes and lane allocation Designing the lane configurations Designing multiple phasing plans Protected and permitted left turns Rights on red Overlapping phasing Slide 26