Maximizing Signal Coordination Efficiency in Traffic Systems

1. Topic 3 Basic Signal Timing and Coordination Principles

2. Signal System Classification • Traditional Systems • Closed-Loop (Field Master) • Centralized Computer Control • Adaptive

3. Signal Timing Process Data Collection Field Implementation Signal Timing Development

4. Basic Terminology • Cycle • Phase Split • Phasing Sequence • Offset • Force-off

5. Cycle Length and Split • Cycle Length All signals must have a common cycle length to achieve coordination • Split Split = Green + Yellow + All-red

6. Signal Coordination Intersection #1 Intersection #2 East Bound

7. Offset • Offset is the time difference between two reference points • Offset must be specified by • Phase • Begin/end phase • Offset = 0 ~ cycle length

8. Offset Local zero Local zero ф 2,5 ф 1,5 ф 1,5 ф 2,6 ф 4,8 ф 2,6 ф 4,8 ф 3,7 When the local zero occurs at 40 sec of the master clock We say the Offset = 40 sec

9. Time-Space Diagram One-way Street Y=5 G=25 R=30 #1 2 8 2 8 4 4 6 6 EB Band G=35 Y=5 R=20 #2 2 2 8 4 8 4 6 6 Time

10. Time-Space DiagramTwo-way Street #1 Y=5 G=25 R=30 2 8 2 8 4 4 6 6 EB Band WB Band G=35 Y=5 R=20 2 2 #2 8 4 8 4 6 6 Time

11. Questions Question 1: 2 and 6 at intersection #1 turn to green at 60 sec, 2 and 6 at intersection #2 turn to green at 20 sec, what are the offset s at the two intersections, assuming the offset is referenced to the start of green of 2 and 6? Question 2: Given the offsets number in Q1, what will the offsets be if the offsets are referenced to the end of green of 2 and 6? Question 3: If the travel speeds are different for the two directions, will it affect the above offset results?

12. Offset and Transition • Synch point/clock: the time all offsets are referenced to. It is also called Master Clock Zero. It is usually set at 12:00 – 3:00 a.m. when traffic is light. 12:00 a.m. (Master Zero) Master Zero Master Zero Master Zero Local Zero Local Zero Local Zero Offset

13. Example • If the Synch point is set at 3:00 a.m., for a signal operating at an 90-sec cycle and an offset of 40, what would be the master clock timer and the local clock timer at 11:20 a.m.?

14. Transition Methods • Transition occurrences • Plan change • Preemption • Pedestrian • Transition methods/algorithms • Dwell • Max Dwell • Add • Subtract • Shortway

15. Example

16. Offset and Transition 1 1 2 2 #1 8 4 6 5 6 5 WB: 8 sec EB: 20 sec #2 2 8 4 8 4 6

17. Bandwidth(Dual LT Leading) 1 1 2 2 #1 8 4 6 5 6 5 WB: 8 sec EB: 20 sec #2 2 8 4 8 4 6

18. Bandwidth - Adjusted(Dual LT Leading) 1 1 2 2 #1 8 4 6 5 6 5 WB: 12 sec EB: 20 sec #2 2 8 4 8 4 6

19. Bandwidth - Initial(Lead/Lag) 1 1 2 2 #1 8 4 6 5 6 5 WB: 12 sec EB: 20 sec #2 2 8 4 8 4 6

20. Bandwidth - Adjusted(Lead/Lag) 1 1 2 2 #1 8 4 6 5 6 5 WB: 20 sec EB: 20 sec #2 2 8 4 8 4 6

21. MOEs • Bandwidth Concept (PASSER II) • Bandwidth, seconds • Bandwidth Efficiency = Bandwidth/Cycle • Attainability = Bandwidth/gmin • System-Wide Delay (Synchro) • System-wide Stops and Delay (TRANSYT-7F)

22. Yellow Trap “Yellow trap” is a situation faced by a left-turn movement when the display of “yellow” occurs to both the left-turn phase and the adjacent through phase, but the opposing through is not terminating. (1) (3) (2) (5) (4)

23. Dallas phasing has louver that through vehicles cannot see

24. Left-turn phase about to end

25. Through movements move both directions. Left-turn yield to opposing through.

26. Yellow trap occurs when the leading left-turn sees yellow and thinks the opposing through phase will also end

27. Dallas phasing does not display yellow, and left-turn sees green ball and is supposed to still yield.

28. When left-turn sees yellow, the opposing phase also about to end

29. Main street phases end, side street phases begin

30. Yellow Trap • Only the leading left-turn has the “yellow trap” with protected/permitted phasing • Dallas Phasing solves the "yellow-trap" problem by holding a solid green indication. • Louvers are used to shield the left-turn display so that the green display in the left-turn signal cannot be easily seen by thru drivers. • When can a “yellow trap” occur with standard PPLT with left-turns leading or lagging? http://projects.kittelson.com/pplt/LearnAbout/Learn3.htm http://projects.kittelson.com/pplt/displays/dallas_doghouse_lag.htm

31. Summary • What is “Yellow Trap” and when it occurs? • What is the main purpose of using “Lead-Lag” phasing? Can “Lead-Lag” phasing increase an intersection capacity? • What is the exception that a different cycle length can be used at an intersection while still maintaining coordination? • Offset • Bandwidth • Time-Space Diagram

32. Lab Exercise • Use the Kietzke system (3 signals) to perform the following exercise. • Use the Synchro offset optimization (keep cycle length and splits unchanged) and answer the following questions: • What are the phasing sequences at each intersection? • How are the offsets referenced and what are the offsets? • Examine the timing solution and indicate where stops may occur if driving on the main street both directions. • Can you further improve the bandwidth by changing the phasing sequences from Synchro? Answer the same questions above. • Which intersection is controlling the bandwidth?

33. Lab Exercise • Use the Boulder Highway system (3 signals) to perform the following exercise. • Understand the existing timing sheets and compare with Synchro coding. • Use the Synchro offset optimization (keep cycle length and splits unchanged) and compare Synchro timing solution with the existing (bandwidth) • How was the phasing sequence changed at each signal? Can you further improve the bandwidth by changing the phasing sequences from Synchro? • Which intersection is controlling the bandwidth? • Try only with two intersections (Harmon and Tropicana) and see how the solution changes.

34. Signal Timing Sheets (NextPhase) Boulder Hwy/Tropicana Intersection • 1.1 – Schedule of timing plans • 2.3.x – Information of a timing plan: cycle, split, offset, sequence • 2.4.x – Phasing sequence • 2.5.x – Phase data (min green, yellow, all-red etc.) • 4.2.1- Phase designation (direction/movement) and ring structure

35. Lead/Lag Phasing WB = 36 sec EB = 16 sec

36. EB = 16 sec WB = 45 sec