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
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
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? Critical Volumes
3 EB L, EBT + WB TR, NB LTR
Critical Volumes
EW (1.32) = 862 or 1100
275(1.05) = 289 EBL
NB (1.05) +25(1.32) = 980
Vc = 1100/ /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
Phase
Green
Yellow
All red
EBL 17 3 1
EBT & WBTR 32 NB 19

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

12. Prob 21-5 Peds NB WALKmin = 3.2 + 0.27*Nped For WE<= 10ft
Flashing Don’t walk = L/Sp NB
WALKmin = *200/80 = 3.9s
Flashing Don’t walk = 76/3.2 = 23.8s
19+4>? 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 = = 98s