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Traffic Signal Systems Operations and Design: Isolated Intersections
4. How can you verify that a vehicle call has been placed?
5. Describe some of the observations that you have made on the response of the controller timing
processes to vehicle calls.
There are a number of traffic controllers that are in common use today, including those manufactured
by McCain, Siemens, Peek, Naztec, and Econolite. There are three primary types, Type 170 and
2070 controllers, NEMA controllers, and advanced traffic controllers (ATC). In this activity, you will
discover (explore) a NEMA controller produced by Econolite known as the ASC/3.
The features and functions of the ASC/3 are not dramatically different from other actuated traffic
controllers. Using the ASC/3 controller emulator, including its functionality and the kinds of
information that it displays, will help you to understand more about traffic signal timing and the
controller processes that determine how effective a timing plan will be. While other types of controllers
are used in this book, the ASC/3 controller emulator provides a transparent way to learn more about
traffic controllers in general.
The video that you will watch as a part of this activity shows the ASC/3 controller in operation (see
Figure 83). The left portion of Figure 83 shows the display for a tool that is commonly used to test the
functions of a traffic controller known as a “suitcase tester.” This tester derives its name because it is
often stored in a suitcase box for easy portability. The display status for each vehicle phase is shown
at the top of the screen (green, yellow, red). In this example, phase 2 is currently green while the other
phases display red. Detector calls can be placed by clicking on the boxes at the bottom of the left
portion of the screen (where the cursor is shown in the figure).
The right portion of the figure shows the status display screen for an ASC/3 controller, as you would
see it in the lab or in the field. For each phase, you can see the phase status and the presence (or not) of
a vehicle call. Phase 2 is currently active (“G” for green). You can also observe the status for various
timers for rings 1 and 2, and as well as the phase that is currently active. Here, phase 2 is timing in
ring 1 and the vehicle extension timer (EXT1) is at 2.8 seconds. The maximum green timer (MAX1)
is at zero.
A
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19: T
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ASC/3 T
raffic
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ontroller