Traffic Signal Timing Design Part I Steps in

Traffic Signal Timing Design Part I

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 2

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 3

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 4

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

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 6

Phase Diagram φ1 φ2 Slide 7

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 8

Critical Lane Volumes SB TH 550 WB TH 700 φ1 φ2 V 1= max{700, 450} = 700 V 2= max{550, 300} = 550 EB TH 450 NB TH 300 Slide 9

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 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

Clearance Interval τmin = tr + [(W+L)/u 0] + [u 0 /(2 a)] 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) = tr is driver’s reaction time (sec) = a is deceleration rate (ft/s 2 or m/s 2) = 10 fps 2 Slide 12

Length of All-red versus Yellow w τ = 4. 2 seconds w Yellow = 3. 5 seconds w All Red = 0. 7 seconds w Notes n n Typical values for yellow 3 to 4 seconds; use judgment remaining clearance interval time is all red Slide 13

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 14

Lost Time w L = l 1 + l 2 w assume start and end loss = 2 sec per phase (make assumption if not given in problem) w L = 2 + 0. 7+ 2 + 0. 7 = 5. 4 seconds Slide 15

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 16

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

Webster’s Formula for Optimum Cycle Length 1. 5 L + 5 Co = 1 - yi w Notes n n as L gets larger Co gets larger as volumes get larger Co gets larger Slide 18

Webster’s Formula for Optimum Cycle Length 1. 5 L + 5 Co = 1. 5*5. 4 + 5 = 1 - yi = 1 -[(700/1900)+(550/1900)] = 38. 5 sec. 40 sec w Notes n Cycle is typically rounded up to nearest 5 seconds Slide 19

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 20

Allocating Green Time g. T = C - L = gi = g. T (yi / Y) Y = Syi Slide 21

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 22

Display Green (as opposed to effective green) G i = g i + l i - τi G 1 = 19. 4 + (2+0. 7) - (3. 5 +0. 7) = 17. 9 seconds G 2 = 15. 2 + 2. 7 - 4. 2 = 13. 7 seconds Note the AR is added and then subtracted Slide 23

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 24

35. 8 39. 3 40. 0 22. 1 40. 0 17. 9 21. 4 Timing Diagram Slide 25

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