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Subproblem 5b - Page 1 of 7 |
ID# C305B01 |
Sub-problem 5b:
Three-Phase Traffic Signal
Control with a Protected Westbound Left Turn
Step 1. Setup
Having established
the need for westbound left-turn protection in Sub-problem 5a, we will now
examine the HCM treatment of protected left turns. Because of the isolated
and high speed characteristics of this intersection, we would expect to
implement a control scheme in which all movements are traffic-actuated. We
will, however, limit the investigation to pre-timed control in this
sub-problem, leaving traffic-actuated control for Sub-problem 5c. There are
two reasons to separate the control treatment into different sub-problems.
First, we can get a better idea of how these control modes differ if we
examine both of them in detail. Second, the timing plan based on pre-timed
control is often a useful input into the analysis of traffic-actuated
operation.
Consider:
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During this sub-problem, signal timing strategies are
explored. There are three different schools of thought on the issue: one
thought is to equalize the v/c ratio for each approach, another is to
equalize the delay, and the last is to minimize delay. What pros and cons
do you think are associated with each of these strategies? Considering
roadway volumes, lane groupings, and other issues that may affect each of
the parameters, do you think one solution will always be desirable? |
| After you have read through this sub-problem, reflect
on the first question and see if your initial thoughts still hold true. |
Discussion:
 Take
a few minutes to consider these questions. Click continue when you are
ready to proceed. [
Back ] to Sub-Problem 5a [
Continue ] with Sub-Problem 5b |
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