Problem 1: Analysis of the U.S. 95/Styner-Lauder Avenue Intersection

We will now integrate the results from the three computations, considering the intersection U.S. 95/Styner/Lauder under TWSC and signal control.  

Let's begin with a comparison of the overall delay experienced by all drivers who would use the intersection. This intersection delay is calculated explicitly as part of the HCM method for signalized intersections. For the TWSC intersection, we will assume that the delay is zero for major street through and right turn vehicles and compute a weighted average of delay for all vehicles entering the intersection. But while we can compute the average intersection delay for a TWSC intersection, we should note that the HCM explicitly does not define level of service for the intersection as a whole. This fact should encourage the user to look carefully at the operation of each minor movement. We should also be reminded that both v/c ratio and queue length should be considered when reviewing the overall performance of the TWSC intersection.

When a signal is added, the delay is shifted from some movements to other movements. In this case, the northbound and southbound traffic on U.S. 95 experience no delay when the side streets (the eastbound and westbound movements) are stop sign controlled. But when a signal is added, these movements will also experience some delay. In fact, the average delay for all vehicles increases by a small amount when the intersection control is changed from TWSC to signal control.

The benefits of the signalized control, however, are shown when the future conditions are considered. The additional delay for all vehicles increases by a small amount, while for TWSC the delay increases significantly from about 10 seconds per vehicle to about 32 seconds per vehicle.

This difference is more dramatic when considering individual movements or lane groups. For example, for existing volumes, the WB LT movement would experience almost a 50 percent decrease in delay (from 36 seconds to about 19 seconds) if the intersection were signalized.