Lec 19, Ch.17, pp.453-461: Sample simple timing problems (Objectives)

Lec 19, Ch.17, pp.453-461: Sample simple timing problems (Objectives)

Master the steps of simple signal timing through 4 sample problems in the textbook

What we cover today in class…

Review of the assumptions and steps Sample problem 1 Sample problem 2 Sample problem 3 Sample problem 4

Simple signal timing: getting startedThis simple method gives you the direction for detailed signal timing. This method uses the formula for the “time budgeting” method as the basis. (Equation 16-11 NOT Equation 17-11 as shown in the text.)

Assumptions:

S = 1900 pcphgpl, but use 85% of it. Hence, s = 0.85x1900 = 1615 pcphgpl (h = 3600/1615 = 2.23 sec/veh)

12-ft lane width, no parking or local buses, 5% heavy vehicles, +1% grade, a CBD location, and a lost-time of 3 seconds

)/(16151

3

)/3600)(/(1

cvPHF

VN

hcvPHF

VNt

Ccc

Ldes

…(Eq. 17-9)

Simple signal timing: getting started (cont)The effect of turning vehicles are included in Vc by multiplying ELT and ERT as shown in Table 17-3 and 17-4 (Note these are different from the ones we use for computing fHV in capacity analysis.)

Simple signal timing: getting started (cont)1. Develop a reasonable signal phase plan. Decide

how to deal with left-turning vehicles.

2. Convert all left-turning and right-turning volumes to through car equivalents (tcu’s) using Tabs 17-3 and 17-4.

3. Establish a reasonable phase plan. Determine the actual sum of critical lane volumes, Vc, using this plan. Check the sum of critical lane volumes in tcu’s for reasonableness.

4. Using Equation 17-9, determine the desirable cycle length based on a desired v/c ratio (0.85-0.90), the PHF.

5. Allocate the available effective green time within the cycle in proportion to the critical lane volumes (in tcu’s) for each signal phase.

for

Sample Problem 1, p.453

Recommend an appropriate signal timing for the intersection shown below. Solution:

Through car equivalent (tcu) volumes to determine critical lane or lane group (Step 2)

Sample problem 2, p. 455

PHF = 0.85

v/c = 0.85

Pedestrian = modest

Solution:

Through car equivalent (tcu) volumes to determine critical lane or lane group (Step 2)

Sample problem 3, p. 457

Through car equivalent (tcu) volumes to determine critical lane or lane group (Step 2)

Sample problem 3, Solution

Sample problem 4, p. 459

Through car equivalent (tcu) volumes to determine critical lane or lane group (Step 2)

Sample problem 4, Solution