Subproblem 4a - Page 1 of 4
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.
The heavy northbound congestion evident in the current operation in
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.