1. Signal timing CTC-340

2. Key Elements Development of safe and effective phase plan and sequence Determination of vehicle signal needs –Timing of yellow and all red clearance intervals –Determination of the sum of the critical lane volumes –Determination of lost time per phase and per cycle –Determination of an appropriate cycle length –Allocation of effective green to various phases

3. Key Elements Determination of ped needs –Determine the minimum time for ped green –Check to see if veh greens met minimum ped needs –If ped needs unmet -> adjust veh green times or install actuators to ensure ped safety Usually not a single “right” answer

4. Treatment of LT –2 guidelines for whether or not a particular LT requires protected or partially protected phase v LT >= 200 vph v LT *(v o /N o ) >= 50,000 v o = opposing TH movement flow rate N o = number of opposing TH lanes –Protection rarely given when v LT < 2 veh/cycle –LT that sneak thru intersection after opposing traffic (sneakers – can average 2/cycle)

5. Treatment of LT –Usually provide LT lanes in both directions Keeps opposing traffic in lines –When should permitted LT phasing be used –F18.1 –Unrestricted sight distance for LT veh –Fewer than 8 accidents involving LT veh in 3 years at any one approach

6. Treatment of LT –Guidance for choosing between protected and compound –Must meet 2 of 3 LT flow rate > 320 vph Opposing flow rate >1100 vph 2 or more LT lanes Fully protected recommended if any one of these is met –3 opposing traffic lanes with opposing spd >45 mph –LT flow rate >320 vph & HV>2.5%

7. Treatment of LT –Opposing flow rate >1100 vph & HV > 2.5% –7 or more LT accidents within 3 years under compound phasing –Average stopped delay to LT traffic is acceptable for fully protected phasing and engineer judges that additional accidents would occur under compound phasing May need to ban LT traffic entirely (Arterial

8. General Considerations in Signal Phasing –1 Phasing can be used to minimize accident risks by separating competing movements –Additional phases add delay and need to be weighed against gains in safety –Increasing phases increases lost time but also increases LT sat flow rates –All phasing must be implemented in accordance with MUTCD and have signage, markings, and signal hardware –Phase plan must be consistent with intersection geometry, lane use assignments, volumes and spds, and ped crossings

9. Phase and Ring Diagrams F 18.2 Phase diagram – shows all movements in a given phase within a single block of the diagram Ring diagram – shows which movements are controlled by which ring of the controller movements –Rings generally control 1 set of signal faces

10. Phase and Ring Diagrams F18.3 – simple 2 phase explain ring and phase diagrams F18.4 Exclusive LT phasing F18.5 Lead / lag LT green F 18.6 Leading Green LT F 18.7 8 phase Actuated F 18.8 Exclusive Ped Phase

11. Right Turn Phasing Protected RT only when high Ped # Compound RT with protected LT on opposing streets RTOR –Use unless 1 of following Restricted sight distance fro RT High speed conflicting TH traffic High flow rate of conflicting TH traffic High ped flow in crosswalk

12. Determining Veh signal req’t Change Interval –MUTCD does not require Y and AR but does recommend them –MUTCD does prohibit Y to mark transition from R to G –Time for a vehicle 1 stopping distance away to enter the intersection under Y (front tires cross stop bar)

13. Determining Veh signal req’t y = t + 1.47S 85 /(2a +(64.4*0.01G)) t = reaction time (s) S 85 = 85 th percentile spd of approaching traffic or spd lmt a = decel in ft/s^2 G = grade, %

14. Determining Veh signal req’t –Clearance time Provides sufficient time for veh that has just entered intersection to cross intersection and clear back bumper past curb line before G ar = (w+L)/1.47S 15 S 15 = 15 th percentile spd of approaching traffic or spd lmt If some peds then ar = max((w+L)/1.47S 15, P/ 1.47S 15 ) If significant peds then ar =(P+L)/ 1.47S 15 P = distance from departure stop line to far side of farthest conflicting crosswalk, ft

15. Determining Veh signal req’t –S 85 = S ave + 5 –S 15 = S ave - 5

16. Lost times Start up lost time l1 = 2.0 s/phase e = 2 s/phase l 2 = Y-e Y = y+ar t L = l 1 +l 2 L = Sum(t Li )

17. Critical Volumes Convert all volumes to equivalent thru vehicle units –T 18.1, T18.2 show equivalents for LT,RT traffic volumes Use to find path thru intersection for each phase which has highest volume Determine critical volume for each phase

18. Desired Cycle Length C des = L/(1-(V c /(1615*PHF*(v/c)))) 1615 vphg = sat flow assuming typical conditions of lane width, HV, Grade, parking, peds, buses, area type, lane util L = total lost time per cycle (v/c) = v/c ratio desired for critical volumes –Want to be between 0.85 – 0.95

19. Splitting green g TOT = C-L –g i = g TOT *(V ci /V) –G i = g i -Y i +t Li –Do not do very short phases – confuse drivers

20. Ped Signal Req’ts –Gp = 3.2 +(L/S p ) +2.7*(N ped /W E ) –For W E > 10 ft –Gp = 3.2 +(L/S p ) +0.27*(N ped ) –For W E <= 10 ft –L = length of crosswalk ft –S p = average walking speed ft/s –N peds = # of peds crossing per phase in a single crosswalk –W E = width of crosswalk –3.2 = min start up time for peds

21. Ped Signal Req’ts WALK min = 3.2 + 2.7(N ped /W E ) For W E > 10 ft WALK min = 3.2 + 0.27*N ped For W E <= 10ft Flashing Don’t walk = L/S p G p <= G + Y Either G +Y must be greater or a ped actuator must be provided