Traffic Signal Timing Design Part I

Slide 2 Steps in Designing a Traffic Signal Timing Plan (1/2) 1. Determine lane configurations and lane volumes 2. Propose Phase Plans (provide diagrams) 3. Critical Volumes for each phase (for each proposed plan) 4. Recommend phase plan 5. Clearance Intervals

Slide 3 Steps in Designing a Traffic Signal Timing Plan (2/2) 6. Lost Time 7. Cycle length 8. Green Splits 9. Display Greens 10. Provide Final Timing Diagram Repeat as needed for other lane configurations.

Slide 4 Steps in Designing a Traffic Signal Timing Plan 1. Determine lane configurations and lane volumes 2. Propose Phase Plans (provide diagrams) 3. Critical Volumes for each phase (for each proposed plan) 4. Recommend phase plan 5. Clearance Intervals

Slide 5 Simple Example (no turns) Volumes in vph WB TH 700 EB TH 450NB TH 300 SB TH 550

Slide 6 Steps in Designing a Traffic Signal Timing Plan 1. Determine lane configurations and lane volumes 2. Propose Phase Plans (provide diagrams) 3. Critical Volumes for each phase (for each proposed plan) 4. Recommend phase plan 5. Clearance Intervals

Slide 7 Phase Diagram φ 1 φ 2

Slide 8 Steps in Designing a Traffic Signal Timing Plan 1. Determine lane configurations and lane volumes 2. Propose Phase Plans (provide diagrams) 3. Critical Volumes for each phase (for each proposed plan) 4. Recommend phase plan 5. Clearance Intervals

Slide 9 Critical Lane Volumes WB TH 700 EB TH 450NB TH 300 SB TH 550 φ 1 φ 2 V 1 = max{700,450} = 700 V 2 = max{550,300} = 550

Slide 10 Steps in Designing a Traffic Signal Timing Plan 1. Determine lane configurations and lane volumes 2. Propose Phase Plans (provide diagrams) 3. Critical Volumes for each phase (for each proposed plan) 4. Recommend phase plan 5. Clearance Intervals

Slide 11 Steps in Designing a Traffic Signal Timing Plan 1. Determine lane configurations and lane volumes 2. Propose Phase Plans (provide diagrams) 3. Critical Volumes for each phase (for each proposed plan) 4. Recommend phase plan 5. Clearance Intervals

Slide 12 Clearance Interval τ min = t r + [(W+L)/u 0 ] + [ u 0 /(2a)] W is road width to be cleared (ft or m) = ft L is vehicle length (ft or m) u 0 is approach speed of vehicles (f/s or m/s) = t r is driver’s reaction time (sec) = a is deceleration rate (ft/s 2 or m/s 2 ) = 10 fps 2

Slide 13 Length of All-red versus Yellow  τ = 4.2 seconds  Yellow = 3.5 seconds  All Red = 0.7 seconds  Notes Typical values for yellow 3 to 4 seconds; use judgment remaining clearance interval time is all red

Slide 14 Steps in Designing a Traffic Signal Timing Plan 6. Lost Time 7. Cycle length 8. Green Splits 9. Display Greens 10. Provide Final Timing Diagram Repeat as needed for other lane configurations.

Slide 15 Lost Time  L = l 1 + l 2  assume start and end loss = 2 sec per phase (make assumption if not given in problem)  L = = 5.4 seconds

Slide 16 Steps in Designing a Traffic Signal Timing Plan 6. Lost Time 7. Cycle length 8. Green Splits 9. Display Greens 10. Provide Final Timing Diagram Repeat as needed for other lane configurations.

Slide 17 Webster’s Formula for Optimum Cycle Length 1.5 L + 5 C o = 1-  y i C o is the optimum cycle length (sec) L is the total lost time including all-red (sec) y i is the critical volume to saturation flow for phase i

Slide 18 Webster’s Formula for Optimum Cycle Length 1.5 L + 5 C o = 1-  y i  Notes as L gets larger C o gets larger as volumes get larger C o gets larger

Slide 19 Webster’s Formula for Optimum Cycle Length 1.5 L * C o = = = 1-  y i 1-[(700/1900)+(550/1900)] = 38.5 sec. 40 sec  Notes Cycle is typically rounded up to nearest 5 seconds

Slide 20 Steps in Designing a Traffic Signal Timing Plan 6. Lost Time 7. Cycle length 8. Green Splits 9. Display Greens 10. Provide Final Timing Diagram Repeat as needed for other lane configurations.

Slide 21 Allocating Green Time g T = C - L = g i = g T (y i / Y)Y =  y i

Slide 22 Steps in Designing a Traffic Signal Timing Plan 6. Lost Time 7. Cycle length 8. Green Splits 9. Display Greens 10. Provide Final Timing Diagram Repeat as needed for other lane configurations.

Slide 23 Display Green (as opposed to effective green) G i = g i + l i - τ i G 1 = (2+0.7) - ( ) = 17.9 seconds G 2 = = 13.7 seconds Note the AR is added and then subtracted

Slide 24 Steps in Designing a Traffic Signal Timing Plan 6. Lost Time 7. Cycle length 8. Green Splits 9. Display Greens 10. Provide Final Timing Diagram Repeat as needed for other lane configurations.

Slide 25 Timing Diagram

Slide 26 Reality and Complications  Multiples lanes and lane allocation  Designing the lane configurations  Designing multiple phasing plans  Protected and permitted left turns  Rights on red  Overlapping phasing