Current Practices in Traffic Signal Coordination

1. Kimley-Horn and Associates, Inc. Current Practices in Traffic Signal Coordination Presented by: Wayne Kurfees* Kimley-Horn and Associates, Inc. * PE in AZ, IA, NC, TN, and TX Workshop on Best Practices for Signal Timing and Operations January 9, 2005

2. Disclaimer This presentation is based on current traffic signal coordination practices in the Dallas-Fort Worth Metroplex and may or may not reflect the state of the practice in other areas

3. Wayne’s Rules • The motorists are the ultimate judges of the success of a signal timing project • Before developing the new timing, be sure to understand the timing strategy that’s currently in effect

4. General Philosophies • Progression-based solutions • Continuous green bands if possible, with appropriate consideration of the volumes turning onto and off of the arterial • Otherwise, limit the number of stops for through traffic on the arterial

5. General Philosophies, cont. • Optimize the phase sequence to achieve two-way progression

6. NB NB With One-way Progression

7. SB SB NB NB With Two-way Progression

8. General Philosophies, cont. • When timing a grid of arterials, try to attain interlocking (i.e. both north-south and east-west) progression

9. Plano Carrollton Richardson Addison Garland Farmers Branch Dallas

10. General Philosophies, cont. • Whenever possible, provide seamless progression across jurisdictional boundaries

11. Plano Carrollton Richardson Addison Garland Farmers Branch Dallas

12. Plano Carrollton Richardson Addison Garland Farmers Branch Dallas

13. Plano Carrollton Richardson Addison Garland Farmers Branch Dallas

14. Plano Carrollton Richardson Addison Garland Farmers Branch Dallas

15. Plano Carrollton Richardson Addison Garland Farmers Branch Dallas

16. Plano Carrollton Richardson Addison Garland Farmers Branch Dallas

17. General Philosophies, cont. • Minimize the number of control groups 130” 92” 140” 96”

18. Dallas PGBT Frankford DNT DNT Marsh Midway Trinity Mills N Carrollton “Before” Cycle Lengths (PM Peak): 144 seconds 160 seconds 80 seconds

19. Dallas PGBT Frankford DNT DNT Marsh Midway Trinity Mills N Carrollton “After” Cycle Lengths (PM Peak): 160 seconds 80 seconds

20. Dallas PGBT Frankford DNT DNT Marsh Midway Trinity Mills N Carrollton “After” Cycle Lengths (PM Peak): 160 seconds 80 seconds

21. Richardson Garland Dallas

22. Understand the Client’s Preferences and Limitations • Minimum split times • Coordinated phases • Other through phases • Left-turn phases • Signal sequences • Are lead-lag sequences allowed? • Is it okay to use “Dallas” phasing (or similar techniques) to avoid the yellow trap if the leading side has protected-permissive left turns? • Is it okay for the sequence to change as a function of the timing plan?

23. Understand Any Special Requirements and Limitations of the Particular Brand of System (or Controller Type) • Offset reference points • Are splits in seconds or percent? • Controller-specific limitations • Example: With at least one controller brand, you must add 1 second to the calculated minimum split times

24. Motorist Considerations • Are the progression speeds realistic? • What if the actual platoon speeds are greater than the posted speed limit? • Whenever a major flow has to stop… • A short stop is better than a long one • Try not to have the stop occur at an insignificant minor street • For safety’s sake, the platoon should arrive on red (rather than encounter an unexpected yellow)

25. Pedestrian Considerations • Some locations require full accommodation of the pedestrian intervals • CBD intersections (and other locations with significant pedestrian volumes) • School crossings (at least during the crossing times) • Coordinated phases • Pretimed intersections • Other locations without push buttons (if “where pedestrian movements regularly occur”)

26. Pedestrian Considerations, cont. • Otherwise, the minor-phase split will generally not accommodate the walk and ped clear intervals (and a resynchronization will have to occur after the ped call is served)

27. Use of the Optimization Model • Understand the model’s strengths and weaknesses • Make adjustments as needed to overcome the weaknesses • Use the model as a tool but generally not as the final result

28. Timing Plan Development • Build and calibrate the model • Does it reflect what was observed on the street? • Are progression speeds realistic? • Use a “master” intersection • Make the best use of the model’s optimization • Make adjustments as appropriate

29. Timing Plan Development, cont. • “On-screen” fine-tuning • Eliminate excess time for minor phases • Adjust non-critical phase times to provide the best re-start (i.e. try to avoid the need for multiple stops before “getting back into the band” • Try to make more “good things” happen

30. Timing Plan Development, cont. • Prior to beginning the implementation, review the proposed timing with the client “on-screen”

31. Timing Plan Implementation • Prepare final timing in the appropriate format • Make maximum practical use of automated interfaces between the optimization program and the signal system’s database • Double-check the database before the new timing plans actually operate on the street

32. On-street Fine-tuning • Make the plans “drive” as smoothly as possible for the majority of the motorists • Generally, make use of iterative, small adjustments • Encourage the client’s participation

33. Summary • Good signal timing involves both art and science • Make wise use of the models… but don’t be afraid to use good judgment to improve the on-street result