Analysis - Page 1 of 2
Problem 1: Analysis
of the U.S. 95/Styner-Lauder
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.
Exhibit 1-18. Comparison of Intersection
Control Delay Estimates: TWSC vs. Signal
Control Delay (sec/veh)
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
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.
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