An Overview of Traffic Signal Timing Planning

Understanding the process of designing a traffic signal timing plan involves determining lane configurations, proposing phase plans with diagrams, analyzing critical volumes, recommending a phase plan, and incorporating clearance intervals. Key concepts include considering shared LT+TH lanes, using left turn equivalents for volume allocation, and addressing impacts of LT phases on critical volumes. Through a full example scenario, the importance of factors like lost time, cycle length, and green splits are illustrated.

• Traffic signal timing
• Lane configurations
• Phase plans
• Critical volumes
• Traffic management

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1. Signal Timing: Putting it All Together

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. Critical Concepts to Note Shared LT+TH lanes Use of left turn equivalents for lane volume allocation LT phase impact on critical lane volumes Overlapping phasing: exception to the highest volume is critical rule Every intersection is different in terms of which phase plan works best Slide 4

5. Full Example Speed = 40 mph LT 1 00 TH 300 RT 1 50 LT 200 TH 400 RT 80 SB W B tr= 1 s s=1850 vphpgpl a=10 ft/s2 start and end loss = 3 s 11 foot lanes 24 foot vehicles LT 390 TH 500 RT 1 50 LT 50 TH 200 RT 200 EB NB 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. Full Example 480 200 LT 1 00 TH 300 RT 1 50 LT 200 TH 400 RT 80 SB W B NB & SB Exclusive LT lane Single shared TH & RT lane LT 390 TH 500 RT 1 50 LT 50 TH 200 RT 200 EB NB 390 650 Slide 7

8. Full Example 480 200 LT 1 00 TH 300 RT 1 50 LT 200 TH 400 RT 80 SB W B WB 1. Opposing traffic to LT EB TH+RT=200+200=400 2. 1 LT =2 TH 3. Total equivalent TH 300+2(100)+150 = 650 4. Per lane 650/2 = 325 325 125 225 100 LT 390 TH 500 RT 1 50 LT 50 TH 200 RT 200 EB NB 390 650 Slide 8

9. Full Example 480 200 LT 1 00 TH 300 RT 1 50 LT 200 TH 400 RT 80 SB W B EB 1. Opposing traffic to LT WB TH+RT=300+150=450 2. 1 LT =2 TH 3. Total equivalent TH 200+2(50)+200 = 500 4. Per lane 500/2 = 250 325 125 225 50 100 150 200 250 LT 390 TH 500 RT 1 50 LT 50 TH 200 RT 200 EB NB 390 650 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. Phase Plans for EB/WB Slide 11

12. 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 12

13. Phase Plans for EB/WB Max {(325+50),(250+100)} = 375 Note: Unopposed LT, new lane volumes EB Total equivalent TH 200+1.1(50)+200 = 455 or 228/lane 228 280 = 508 WB Total equivalent TH 300+1.1(100)+150 = 560 or 280/lane Slide 13

14. 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 14

15. Phase Plans for NB / SB Slide 15

16. 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 16

17. Phase Plans for NB / SB Max {(480+390), (650+200)} = 870 Min {200,390} 190 (390-200) Max {390,200} Max {480,460} Max {650,480} CV= 870 CV= 1040 Slide 17

18. 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 18

19. 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 20

20. EB/WB Clearance Interval 1 = tr + [u0 /(2a)] + [(W+L)/u0] W is road width to be cleared (ft or m) = 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) = Slide 21

21. 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

22. Lost Time L = start/end loss + AR Slide 25

23. 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 26

24. Optimum Cycle Length 1.5 L + 5 Co = = 1- yi Slide 27

25. 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 28

26. Green Splits CV1 375 CV2 870 gT = C - L gi = gT (yi / Y) Slide 29

27. 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 30

28. Display Greens Gi = gi + li - i G1 = 12.8 + (3+0.6) - 4.1 = 12.3 seconds G2 = 29.8 + (3+0.8) - 4.3 = 29.3 seconds Slide 31

29. 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 32

30. Timing Diagram Slide 33