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Basic Knowledge of Traffic Signal Control (1)

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

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Basic Knowledge of Traffic Signal Control (1)

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

  2. 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.

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

  4. 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

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

  6. CYCLE Phase 1 Phase 2

  7. S.O.P. 1

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

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

  10. 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

  11. 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)

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

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

  14. 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)

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

  16. Minimum Extension

  17. Gap out

  18. max Max out

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

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

  21. 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

  22. 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

  23. 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

  24. Overlap phasing example 20 35 10 25 90

  25. Overlap phasing example 20 35 55

  26. Overlap phasing example 10 10 25 45

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

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

  29. Signal Coordination

  30. 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

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

  32. Definitions

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

  34. Time-space diagram T i m e Space

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

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

  37. Pretimed signal coordination

  38. Example 4.6 (Textbook)

  39. Example 4.7 (Textbook)

  40. Solution of Example 4.7

  41. Solution of Example 4.7 (cont’d)

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

  43. Source: Synchro Fixed Cycle Coordination

  44. Source: Synchro Fixed Cycle Coordination

  45. Source: Synchro Fixed Cycle Coordination

  46. Source: Synchro Fixed Cycle Coordination

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