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:
-
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.