11 Traffic Signal Control Overview (Traffic Engineering هندسة المرور & Prof. Saad AlGadhi)
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This document discusses traffic signal control and various warrants for installing traffic signals at intersections. It provides an overview of intersection control hierarchy, including basic right-of-way rules and direct assignment of right-of-way via signs. Traffic signalization is the highest level of control. The purpose of traffic signals is to improve safety and decrease travel times by assigning right-of-way. Advantages include orderly movement and reduced accidents, while disadvantages include potential for increased delays and disobedience. Various warrants for installing traffic signals are presented, including vehicular volume, pedestrian volume, coordinated signal systems, and crash experience.
11 Traffic Signal Control Overview (Traffic Engineering هندسة المرور & Prof. Saad AlGadhi)
- 1. CE 436 Traffic Engineering Topic 11: Traffic Signal Control Overview (Ch. 18) Prof. Saad AlGadhi CE 436 –Traffic Engineering King Saud University email: salgadhi@ksu.edu.sa
- 3. Intersection Control Hierarchy Level I: Basic Rules of the Road: Driver on left must yield to one on right Through have ROW over turning vehicles Level II (not Covered): Direct Assignment of ROW: Yield Sign Stop Sign: 2-way and multi-way Level III: Traffic Signalization.
- 4. Level I: Basic Rules of the Road Drivers on conflicting approaches must be able to see each other Visibility Triangle Sight distances must be analyzed to ensure no conflict
- 5. Figure 18.2 Visibility Triangle at an Intersection
- 8. Figure 18.3 Sample Problem: Intersection Sight Distance
- 9. Sample Problem (Figure 18.3) Solution
- 10. Level III: Traffic Signalization
- 11. Traffic Signal Devices One of the most important and effective methods of controlling traffic at an intersection Electrically time device that assigns the right-of- way to one or more traffic streams so that these streams can pass through the intersection safely and efficiently Suitable for: Excessive delays at stop signs and yield signs Problems caused by turning movements Angle and side collision Pedestrian accidents
- 12. History of Traffic Signal Devices First traffic signal (1868): London First electric signal in the US (1914): Cleveland, Ohio First interconnected system of 6 signals (1917): Salt Lake City (manually controlled from a single site) First automated electric timer controlled from a central traffic tower (1922): Houston, Texas First progressive, pretimed system (1928) First actuated controller using pressure detectors (late 20’s) First analog computer system (1952): Denver, Colorado Pilot study using digital computers (1963) Urban Traffic Control System (UTCS) Project (1967): Washington, D.C.
- 13. Purpose of Traffic Signals Improve overall safety Decrease average travel time through an intersection, hence increase capacity Equalize the quality of services for all or most traffic streams Factors to considered: justification (warrants) must be made based on traffic flow, pedestrian safety, accident experience, and the elimination of traffic conflicts.
- 14. Advantages of Signals Provide orderly movement If properly designed signal and intersection, they increase traffic handling capacity Reduce frequency and severity of right- angle accidents When coordinated, provide continuous movement Used to interrupt heavy traffic to permit other traffic to cross (veh. & Ped.)
- 15. Disadvantages of Signals Improperly designed signals cause: excessive delay, which increases driver irritation Excessive Disobedience of its indications Increased use of less adequate routes to avoid the signal Significant increase in rear-end collisions
- 16. Signal Warrants 1) 8-hr vehicular volume (since 1930s) 2) 4-hr vehicular volume 3) Peak hour Volume and Delay 4) Pedestrian Volume 5) School Crossing 6) Coordinated Signal System 7) Crash Experience 8) Roadway Network 9) Intx near HWY-Rail grade crossing
- 17. H.W. # 9-Part 1 Problems Ch. 18 (p. 433) 1. 18-1 2. 18-2
- 18. Further Information Next Slides explaining the warrants are extra reading and not required for this course
- 19. Table 18.5 Warrant 1: Eight-Hour Vehicular Volume
- 20. Figure 18.5 Warrant 2: Four-Hour Vehicular Volume (Source: Used with permission of Federal Highway Administration, U.S. Department of Transportation, Manual on Uniform Traffic Control Devices, Millennium Edition, Figures 4C-1, 4C-2, p. 4C-7, Washington DC, 2000.)
- 21. Figure 18.6 Warrant 3A: Peak Hour Volume (Source: Used with permission of Federal Highway Administration, U.S. Department of Transportation, Manual on Uniform Traffic Control Devices, Millennium Edition, Figures 4C-3, 4C-4, p. 4C-9, Washington DC, 2000.)
- 22. Table 18.6 Warrant 3B: Peak-Hour Delay
- 23. Figure 18.7 Four-Hour Pedestrian Warrant (Source: Manual of Uniform Traffic Control Devices, Draft, Federal Highway Administration, Washington DC, December 2007, Figures 4C-5 and 4C-7.)
- 24. Figure 18.8 Peak-Hour Pedestrian Warrant (Source: Manual of Uniform Traffic Control Devices, Draft, Federal Highway Administration, Washington DC, Draft 2007, Figures 4C-6 and 4C-8.)
- 25. Table 18.7 Warrant 6: Coordinated Signal System
- 26. Table 18.8 Warrant 7: Crash Experience
- 27. Table 18.9 Warrant 8: Roadway Network
- 28. Table 18.10 Warrant 9: Intersection Near a Highway- Rail Grade Crossing
- 29. Figure 18.9 Warrant 9: Railroad Crossings for One-Lane Approaches (Source: Manual of Uniform Traffic Control Devices, Draft, Federal Highway Administration, Washington DC, December 2007, Figure 4C-9.)
- 30. Figure 18.10 Warrant 9: Railroad Crossings for Two or More-Lane Approaches (Source: Manual of Uniform Traffic Control Devices, Draft, Federal Highway Administration, Washington DC, December 2007, Figure 4C-9.)