Repeat Problem 8-16 using saturation flow rates that are 10% higher. What effect does this have on cycle length?

Question

What will be an ideal response?

Answer 1

Assume the following saturation flows:

Through lanes: 1760 veh/h/ln

Through-right lanes: 1540 veh/h/ln

Left lanes: 1100 veh/h/ln

Left-through lanes: 1320 veh/h/ln

Left-through-right lanes: 1210 veh/h/ln



Step 2: Assume an intersection configuration, assign lane groups, and determine

critical volumes.

In this case, each approach was assumed to have one dedicated left-turn

lane, one through lane, and one through-right lane.





Sum Yi = 0.700

Step 4: Calculate lost time per cycle, using Equation 8.8

Assume lost time per phase due to acceleration and deceleration at phase changes

is 3.5 seconds and that an all-red interval of 1.5 seconds is provided at each phase.

Total lost time, L = 20 sec.

Step 5: Calculate cycle length, using Equation 8.6



Step 6: Allocate green times

Allocated times are for green and yellow indications; appropriate length of

yellow interval can be subtracted from the total to give green times.

Total effective green time, Gte = C – L =100 seconds

(G+Y)1 = (0.161/0.700)(100) + 3.5 = 26.5 seconds

(G+Y)2 = (0.234/0.700)(100) + 3.5 = 36.9 seconds

(G+Y)3 = (0.127/0.700)(100) + 3.5 = 21.6 seconds

(G+Y)4 = (0.178/0.700)(100) + 3.5 = 28.9 seconds

Step 7: Ensure that green time required for pedestrian movement is provided,

using Equation 8.12.

Gp1 = 3.2 + (56/3.5) + (0.27)(1200/3600)(120) = 30.0 seconds

Gp2 = 3.2 + (56/3.5) + (0.27)(1200/3600)(120) = 30.0 seconds

Gp3 = 3.2 + (68/3.5) + (0.27)(1200/3600)(120) = 33.4 seconds

Gp4 = 3.2 + (68/3.5) + (0.27)(1200/3600)(120) = 33.4 seconds

Since Gp1 > (G+Y)1 , Gp3 > (G+Y)3 , and Gp4 > (G+Y)4 , the allocated sum

of green and yellow time should be 30.0 seconds for phase 1, 33.4 seconds for

phase 3, and 33.4 seconds for phase 4. Times are typically rounded up to the next

whole seconds; therefore, sum of green and yellow times are: G1 = 30 s; G2 = 37

s; G3 = 34 s; G4 = 34 s, resulting in a total cycle length of C = (30 + 37 + 34 + 34)

+ (4)(1.5) = 141 seconds.

By increasing saturation flow rates by 10%, the recommended cycle

length decreased by 14.5% (from 165 seconds to 141 seconds).