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Signal Design

Signal Design. CTC-340. HMWK. Ch 21 #3, 4, 6. Steps. Convert all volumes to equivalent thru vehicle units T 21.1 , T21.2 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.

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Signal Design

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  1. Signal Design CTC-340

  2. HMWK • Ch 21 #3, 4, 6

  3. Steps • Convert all volumes to equivalent thru vehicle units • T 21.1 , T21.2 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

  4. Desired Cycle Length • Cdes = L/(1-(Vc/(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

  5. Splitting green • gTOT = C-L • gi = gTOT *(Vci/V) • Gi = gi -Yi +tLi • Do not do very short phases – confuse drivers

  6. Ped Signal Req’ts • Gp = 3.2 +(L/Sp) +2.7*(Nped/WE) • For WE > 10 ft • Gp = 3.2 +(L/Sp) +0.27*(Nped) • For WE <= 10 ft • L = length of crosswalk ft • Sp = average walking speed ft/s • Npeds = # of peds crossing per phase in a single crosswalk • WE = width of crosswalk • 3.2 = min start up time for peds

  7. Ped Signal Req’ts • WALKmin = 3.2 + 2.7(Nped/WE) • For WE > 10 ft • WALKmin = 3.2 + 0.27*Nped • For WE<= 10ft • Flashing Don’t walk = L/Sp • Gp <= G + Y • Either G +Y must be greater or a ped actuator must be provided

  8. Prob 21-5 • How many phases? • 3 EB L, EBT + WB TR, NB LTR • Critical Volumes • EW 730+100(1.32) = 862 or 1100 • 275(1.05) = 289 EBL • NB 900+45(1.05) +25(1.32) = 980 • Vc = 1100/2+289+980/3 = 1166

  9. Prob 21-5 • Cdes = L/(1-(Vc/(1615*PHF*(v/c)))) • L = 3*4 = 12 • Cdes = 12/(1-(1166/1615*.95*.9)) = 77.2s • Use 80 sec • gTOT = Cdes – L = 80 – 12 = 68sec • EBL g = 68*(289/1166) = 17s • EBT & WBTR g = 68*(550/1166) = 32s • NB g = 68 *(327/1166) = 19s

  10. Prob 21-5

  11. Prob 21-5 • Peds • WALKmin = 3.2 + 0.27*Nped • For WE<= 10ft • Flashing Don’t walk = L/Sp • EB, WB • WALKmin = 3.2 + 0.27*200/80 = 3.9s • Flashing Don’t walk = 36/3.2 = 11.3s • 32+4>?3.9+11.3 yes EW ok

  12. Prob 21-5 • Peds • WALKmin = 3.2 + 0.27*Nped • For WE<= 10ft • Flashing Don’t walk = L/Sp • NB • WALKmin = 3.2 + 0.27*200/80 = 3.9s • Flashing Don’t walk = 76/3.2 = 23.8s • 19+4>?3.9+23.8 no NB not ok

  13. Prob 21-5 • Retime signals to get same green ratio and satisfy ped needs • NB needs 28s G+Y => 24s green • To maintain ratio • EBL G = 24/19*17 = 22s • EBT &WBTR G = 24/19 * 32 = 40s • Cycle = 24+22+40+12 = 98s

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