Signal Timing: Putting it All Together

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

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.

Critical Concepts to Note Shared LT+TH lanes Use of left turn equivalents for lane volume allocation LT phase impact on critical lane volumes Overlapping phasing: exception to the highest volume is critical rule Every intersection is different in terms of which phase plan works best

Full Example Speed = 40 mph tr= 1 s s=1850 vphpgpl a=10 ft/s2 start and end loss = 3 s 11 foot lanes 24 foot vehicles

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

Full Example 480 200 NB & SB Exclusive LT lane 390 650 480 200 NB & SB Exclusive LT lane Single shared TH & RT lane

Full Example 480 200 WB 1. Opposing traffic to LT EB TH+RT=200+200=400 390 650 480 200 WB 1. Opposing traffic to LT EB TH+RT=200+200=400 2. 1 LT =2 TH 3. Total equivalent TH 300+2(100)+150 = 650 4. Per lane 650/2 = 325 325 225 125 100

Full Example 480 200 EB 1. Opposing traffic to LT WB TH+RT=300+150=450 390 650 480 200 EB 1. Opposing traffic to LT WB TH+RT=300+150=450 2. 1 LT =2 TH 3. Total equivalent TH 200+2(50)+200 = 500 4. Per lane 500/2 = 250 325 225 125 100 250 200 150 50

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

Phase Plans for EB/WB

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

T Phase Plans for EB/WB Max {(325+50),(250+100)} = 375 228 280 Σ = 508 Note: Unopposed LT, new lane volumes EB Total equivalent TH 200+1.1(50)+200 = 455 or 228/lane WB 300+1.1(100)+150 = 560 or 280/lane 228 280 Σ = 508

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

Phase Plans for NB / SB

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

T Phase Plans for NB / SB Max {(480+390), Min {200,390} (650+200)} = 870 Min {200,390} T 190 (390-200) Max {390,200} Max {480,460} Max {650,480} ΣCV = 870 ΣCV = 1040

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

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

EB/WB Clearance Interval τ1 = tr + [u0 /(2a)] + [(W+L)/u0] W is road width to be cleared (ft or m) = L is vehicle length (ft or m) = u0 is approach speed of vehicles (f/s or m/s) = tr is driver’s reaction time (sec) = a is deceleration rate (ft/s2 or m/s2) =

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.

Lost Time L = start/end loss + AR

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.

Optimum Cycle Length 1.5 L + 5 Co = = 1- S yi

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.

Green Splits CV1 375 CV2 870 gT = C - L gi = gT (yi / Y)

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.

Display Greens Gi = gi + li - τi G1 = 12.8 + (3+0.6) - 4.1 = 12.3 seconds G2 = 29.8 + (3+0.8) - 4.3 = 29.3 seconds

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.

Timing Diagram 12.3 15.8 50.0 16.4 45.7 49.2 50.0