Basic Knowledge of Traffic Signal Control (1)

1. Basic Knowledge of Traffic Signal Control (1) Lecture 12 (6/16/11)

3. Pretimed and Actuated Controls • Pretimed Control: Duration of red, green, and yellow intervals are predetermined and fixed. • Traffic-Actuated Control: Duration of green intervals vary according to detected vehicle demand.

4. Advantages of pretimed control • Easy to coordinate with other intersections • Does not rely on detectors • Costs less • Less maintenance

5. Advantages of actuated control • More efficient where traffic demand fluctuates • Greater efficiency at complex intersections • Maximum efficiency at major/minor intersections • Do not need to flash at night

6. Signal timing parameters for both pretimed and actuated controls • Cycle Length • Phase • Interval • Split

7. CYCLE Phase 1 Phase 2

8. S.O.P. 1

9. PHASE Vehicle AR G Y Peds W FDW D INTERVALS

10. SIGNAL TIMING ELEMENTS Split: Allocation of signal timing to each phase

11. Webster’s min delay cycle 1.5 L + 5 Co 1 – S (v/s)c Co = Optimal cycle length for minimum delay L = Lost time per cycle S (v/s)c = sum of the v/s ratios for the critical movements

12. Clearance intervals CP = Change period (sec) t = Perception-reaction time (usually 1.0 sec) v= Approach speed (ft/sec or m/sec) a = Deceleration rate (usually 10 ft/sec2 or 3 m/sec2) g = Grade of approach (decimal) W = Width of cross street (ft or m) L = Length of vehicle (usually 20 ft or 6 m)

13. Traffic actuated control • Adjusts green time continuously based on detected demand. • Can skip phases if no demand.

14. Actuated control parameters • Minimum green • Extension time • Maximum green

15. Pedestrian crossing time Gmin = P + (D/S) – CP Gmin = Minimum length of green (sec) P = Pedestrian start-off time (typically 7 sec) D = Pedestrian crossing distance (ft or m) S = Pedestrian walking speed (usually 4 ft/sec or 1.2 m/sec) CP = Length of vehicle phase change interval (sec)

16. Minimum green Gmin generally ranges from 5 to 25 seconds Gmin = P + (D/S) – CP When pedestrian crossing is considered

17. Minimum Extension

20. Gap out

21. max Max out

22. Dual-Ring Eight Phase Fully Actuated Control 1 2 3 4 5 6 7 8 S.O.P. 10

23. Dual-Ring Eight Phase Fully Actuated Control S.O.P. 10

24. Exercise 1:There is a signalized intersection with dual-ring eight phase fully actuated control. The traffic volumes at a specific cycle are shown below. The land utilization factor for each lane group is assumed 1.0. Please draw the most likely phase sequence. EBLT (2 lanes): 12 vehicles NBLT (1 lane): 4 vehicles WBLT (1 lane): 8 vehicles SBLT (1 lane): 4 vehicles EBTH (3 lanes): 24 vehicles NBTH (2 lanes): 18 vehicles WBTH (3 lanes): 15 vehicles SBTH (2 lanes): 12 vehicles Solution

25. Principles of signal timing • Shorter cycles generally generate less delay • Green intervals should be proportional to traffic demand • Timing must accommodate pedestrians • Phase change intervals must ensure that vehicles can either stop or clear the intersection • Must check the timing in field

26. Principles of signal phasing • Number of phases depends on geometric design, volume, and pedestrians • Increase number of phases to minimize potential hazards • As number of phases increases, total delay generally increases • If possible, use the minimum number of phases to accommodate traffic • Balance safety and efficiency

27. Overlap phasing example 20 35 10 25 90

28. Overlap phasing example 20 35 55

29. Overlap phasing example 10 10 25 45

30. Exercise 2: Draw a phase sequence with overlap phasing. 15 30 20 30 Solution: 15 5 30

31. Basic Knowledge of Traffic Signal Control (2) Lecture 13 (6/16/11)

32. Signal Coordination

33. Objective of signal coordination Allow platoon of vehicles to clear as many signals as possible without interruption Meet the expectation of the general public Minimize stops and delays at signalized intersection Reduce congestions Reduce crashes Improve travel time

34. Design of signal coordination • System cycle length • Split • Offset

35. Definitions

36. Time-distance (time-space) diagram of interrupted flow

37. Time-space diagram T i m e Space

38. Time-space diagram T i m e Green Band Offset3 Offset2 Offset5 Offset4 Offset1 Space

39. Pretimed signal coordination Offset at D Band width Band speed Offset at C Band width Band speed

40. Pretimed signal coordination

41. Example 4.6 (Textbook)

42. Example 4.7 (Textbook)

43. Solution of Example 4.7

44. Solution of Example 4.7 (cont’d)

45. Example of a fixed cycle coordination Source: Synchro Fixed Cycle Coordination

46. Source: Synchro Fixed Cycle Coordination

47. Source: Synchro Fixed Cycle Coordination

48. Source: Synchro Fixed Cycle Coordination

49. Source: Synchro Fixed Cycle Coordination