Isolated Actuation, plus The Dilemma Zone Dilemma

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

2. 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 TRB Signal Timing Best Practices Workshop 2005

3. 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: TRB Signal Timing Best Practices Workshop 2005

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

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

6. 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 TRB Signal Timing Best Practices Workshop 2005

7. 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: TRB Signal Timing Best Practices Workshop 2005

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

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

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

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

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

13. 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. TRB Signal Timing Best Practices Workshop 2005

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

15. 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 TRB Signal Timing Best Practices Workshop 2005

16. 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? TRB Signal Timing Best Practices Workshop 2005

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

18. 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 TRB Signal Timing Best Practices Workshop 2005

19. 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 TRB Signal Timing Best Practices Workshop 2005

20. 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 TRB Signal Timing Best Practices Workshop 2005

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

22. 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 TRB Signal Timing Best Practices Workshop 2005