For the geometric and traffic characteristics shown below determine a suitable signal phasing system and phase lengths for the intersection using the Webster method. Show a detailed layout of the phasing system and the intersection geometry used.



Assume the following saturation flows:

Through lanes: 1600 veh/h/ln

Through-right lanes: 1400 veh/h/ln

Left lanes: 1000 veh/h/ln

Left-through lanes: 1200 veh/h/ln

Left-through-right lanes: 1100 veh/h/ln



What will be an ideal response?


Step 1: Calculate equivalent hourly flows



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.



Step 3: Assume a phasing scheme and determine Yi , sum of critical ratios

Assume four phases as follows:



Sum Yi = 0.770

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 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 =135 seconds

(G+Y)1 = (0.177/0.770)(135) + 3.5 = 34.5 seconds

(G+Y)2 = (0.257/0.770)(135) + 3.5 = 48.5 seconds

(G+Y)3 = (0.140/0.770)(135) + 3.5 = 28.0 seconds

(G+Y)4 = (0.196/0.770)(135) + 3.5 = 37.9 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)(155) = 33.2 seconds

Gp2 = 3.2 + (56/3.5) + (0.27)(1200/3600)(155) = 33.2 seconds

Gp3 = 3.2 + (68/3.5) + (0.27)(1200/3600)(155) = 36.6 seconds

Gp4 = 3.2 + (68/3.5) + (0.27)(1200/3600)(155) = 36.6 seconds

Since Gp3 > (G+Y)3, the allocated sum of green and yellow time for phase

3 should be 36.6 seconds. Times are typically rounded up to the next whole

seconds; therefore, sum of green and yellow times are: G1 = 35 s; G2 = 49 s; G3 =

37 s; G4 = 38 s, resulting in a total cycle length of C = (35 + 49 + 37 + 38) +

(4)(1.5) = 165 seconds.

Trades & Technology

You might also like to view...

The four commonly used classifications of soils arranged in order of decreasing particle size are

A) gravel, silt, clay, and sand. B) gravel, sand, silt, and clay. C) gravel, sand, clay, and silt. D) gravel, silt, sand, and clay. E) none of the above.

Trades & Technology

Convert the circuits in Fig. 2.112 from Y to ?.

Trades & Technology

Types of communications include ________

A) Nonverbal B) Written C) Verbal D) All of these

Trades & Technology

Technician A says that a muffler is usually located on the discharge side of a compressor. Technician B says that a muffler can sometimes be located on the intake side of a compressor. Who is correct?

a.Technician A only b.Technician B only c.Both A and B d.Neither A nor B

Trades & Technology