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190
Traffic Signal Systems Operations and Design: Isolated Intersections
5. Do you think that the quality of service provided to the motorist is good or not? Why or why not?
6. If the phase terminates too early or extends too long, what solutions should be considered?
In this activity, you will consider two cases, one in which the southbound approach has a 22 foot
detection zone and another in which the approach has a 66 foot detection zone, each representing a zone
length sometimes used in practice. In both cases, the detection zones end at the stop bar. See Figure
115. The vehicle extension time and minimum green time are set to
zero. The detectors are both operating in presence mode. You will
observe how and when the phase terminates for both cases, and the
status of the controller at several points in the simulation.
It is important to understand that both detectors are operating in
the presence mode. This means that as long as the detection zone
is occupied, a call is sent to the controller for the assigned phase.
If a constant call is sent to a phase that is green, it will continue to
remain green as long as the phase has not “maxed out.”
The vehicle extension time and minimum green time parameters
have both been set to zero for phase 4, the phase serving the
southbound through approach movement. This means that you
need to focus only on the detection zone length and how it affects
the duration of the green indication.
Vehicles are present on the southbound approach on Line Street
(phase 4), and the eastbound and westbound approaches on State
Highway 8 (phases 2 and 6).
Figure 115.
Two detection zone
alternatives on Line
Street SB approach
Open the movie file, A32.wmv. Pause the playback. The simulation window shows the animation of
vehicles traveling through the intersection as well as other data (see Figure 116):
•
The current simulation time is noted in the lower left
•
The detection zones (and their numbers) are shown in each approach lane as boxes
A
ctivity
32: R
elating
the
L
ength of
the
D
etection
Z
one
to
the
D
uration of
the
G
reen
I
ndication