Subproblem 4a - Page 1 of 4

ID# C304A01

Sub-problem 4a: Potential Left-Turn Capacity

Step 1. Setup

We will now look at the operation of the northbound left-turn movement and consider the potential left-turn capacity of that movement as it crosses the eastbound movement.

Exhibit 3-26 shows the northbound left-turn queue at the Okeechobee Road Intersection. Observe the number of heavy vehicles in the traffic stream, each of which will require longer gaps in order to pass through the conflicting traffic stream. Notice also the skid marks in the foreground, possibly indicating that at least some northbound left turns are attempted through eastbound vehicle gaps that are too short. This observation may be further confirmation of the capacity deficiency for the northbound left turns that seems apparent in the picture.

Exhibit 3-26. Northbound Left Turn
Click to enlarge

The heavy northbound congestion evident in the current operation in Exhibit 3-26 suggests that the capacity of the northbound left turn should first be examined by the basic principles set forth in the HCM before the full procedure is invoked by software. This step will give us a better understanding of the basic relationships that apply to TWSC control.

Consider:

	What volume-related factors affect the northbound left-turn movement capacity?
	What geometry-related factors affect the northbound left-turn movement capacity?
	How could we take into account the separation of the roadways?

Discussion:
Take a few minutes to consider these questions. Click continue when you are ready to proceed.

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