1. TRB Signal Timing Best Practices Workshop 2005 Isolated Actuation, plus The Dilemma Zone Dilemma Rick Denney Iteris

2. TRB Signal Timing Best Practices Workshop 2005 Actuated Controller Settings include Minimum Green (or Initial) Extension (or Passage) Volume-Density: Variable Initial Volume-Density: Variable Extension Maximum Green (or Maximum Extension) Coordination Settings

3. TRB Signal Timing Best Practices Workshop 2005 Minimum Green Settings Clears queue from stop line to first detector Typical formula (variations do exist) is the sum of the startup time plus the time needed for each car in queue:

4. TRB Signal Timing Best Practices Workshop 2005 Volume Density: Variable Initial Minimum initial Added initial (added per actuation) Maximum initial

5. TRB Signal Timing Best Practices Workshop 2005 Variable Initial—Diagram Vehicles Detected Minimum Initial Extension Vehicles Detected Each actuation increases initial Maximum Initial Controller Time Settings Added Initial RedGreenYellow

6. TRB Signal Timing Best Practices Workshop 2005 Variable Initial Settings Used in absence of stop-line detector Add to the minimum green for each car that passes over loop Typically “added-per-actuation” = ~ 2 sec. Minimum initial = minimum green Maximum initial is 2 times the number of cars that will fit between stop line and loop

7. TRB Signal Timing Best Practices Workshop 2005 Extension Maintains green when density is high Typically long enough for extending vehicle to clear dilemma zone With dilemma-zone detection, extension is part of the design With presence detection, extension long enough for expected gap:

8. TRB Signal Timing Best Practices Workshop 2005 Extension Extension = X – speed/(length of loop + car), where X depends on your goals… X

9. TRB Signal Timing Best Practices Workshop 2005 Extension Extension value a trade-off in heavy traffic… X?

10. TRB Signal Timing Best Practices Workshop 2005 Volume Density: Variable Extension Variable extension (gap reduction) Time before reduction Minimum gap Time to reduce, or reduce by

11. TRB Signal Timing Best Practices Workshop 2005 Variable Extension—Diagram Minimum Gap Initial Green Vehicles Detected Extension Time to Reduce, or Reduce By Time Before Reduc- tion Controller Time Settings First Opposing CallGap Out GreenYellow

12. TRB Signal Timing Best Practices Workshop 2005 Variable Extension—Diagram Minimum Gap Initial Green Vehicles Detected Extension Time to Reduce, or Reduce By Time Before Reduc- tion Controller Time Settings First Opposing CallGap Out GreenYellow Queue Clearance Queue Gone

13. TRB Signal Timing Best Practices Workshop 2005 Variable Extension Settings Extension Generous for queue departure: ~2.5-3 sec. Time Before Reduction Long enough to clear typical queue Time to Reduce Typically 5-10 sec. Minimum Extension Short enough to only allow tight gaps: ~2 sec.

14. TRB Signal Timing Best Practices Workshop 2005 Maximum Green—Diagram Vehicles Detected Maximum Green Maximum Extension Initial or Minimum Green Extension Phase timer reaches Max, phase maxes out and terminates Controller Time Settings GreenYellowRed

15. TRB Signal Timing Best Practices Workshop 2005 Maximum Green Doesn’t care if you have dilemma zone protection Doesn’t care if the queue is cleared Doesn’t care if a platoon is arriving, but Often the only thing preventing insane cycle lengths

16. TRB Signal Timing Best Practices Workshop 2005 Some Biased Questions Does the dilemma zone really exist? What is the real purpose of dilemma zone protection? Prevent accidents from cars going too fast, too close? Reward fast drivers with longer green?

17. TRB Signal Timing Best Practices Workshop 2005 Is There A Better Way? To improve safety without rewarding speeders? To keep cars from entering intersection dangerously?

18. TRB Signal Timing Best Practices Workshop 2005 The Main Problem Dilemma zone protection set up at a point where cars should start to stop, but It’s when they go that causes the problem DZ makes the decision to extend the green 6-9 seconds before the problem Lots of detection infrastructure required, and sluggish timing unavoidable

19. TRB Signal Timing Best Practices Workshop 2005 A Solution? (aka Research Needs) Delay the crossing green to prevent accidents, but Don’t extend the green to reward the speeder Ergo: A variable red clearance interval

20. TRB Signal Timing Best Practices Workshop 2005 Variable Red Clearance: Advantages Not concerned with stopping distance— stopping cars are already stopping Concerned with cars that are still going at the end of the yellow Measured close to the stop line, where detection is cheap and easy Detects problems where they exist instead of projecting them 6-9 seconds back

21. TRB Signal Timing Best Practices Workshop 2005 Disadvantages Controllers don’t work that way Needs research to discover hidden disadvantages

22. TRB Signal Timing Best Practices Workshop 2005 Summary (Yup, this is biased, too) Old methods used fancy timing to work with limited detection New methods use fancy detection layouts that add more and more green time to serve less and less traffic None solve the problem: Clearance problems should affect clearance intervals, not green time