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Chapter 5: The Simulation Environment: Learning to See a Traffic Signal System
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In Chapter 5, you will learn how the simulation environment can help you to visualize traffic control
processes. Simulation, or microsimulation as it is sometimes called, is a very detailed and realistic
representation of a transportation system. It is detailed enough that you can directly view individual
vehicles traveling along an arterial or through an intersection. Many simulation models even provide
for a three-dimensional perspective of a network. In microsimulation models, the decisions of individual
drivers are modeled: how fast to travel, how far behind a leading vehicle to follow, when to change lanes,
when to stop when the yellow indication is displayed, and when to accelerate when the green indication
is displayed. These are the kinds of driver decisions that are modeled in a microsimulation model such as
VISSIM, often every tenth of a second in simulation time.
But your work is not about learning how to use a specific simulation model, though the activities that you
will complete are conducted using the VISSIM microsimulation model. Nor is it about using a specific
traffic signal controller. Rather it is about observing the flow of individual vehicles and how they interact
with the individual controller timing processes. This is the perspective that the traffic engineer has when
he or she is standing in the field: how is the traffic flowing and what are the timing processes that we can
change in the traffic controller to help make traffic flow better?
You will use this simulation environment to directly see the results of the phasing plans and timing
parameters that you select. Using VISSIM’s animation and movie files, you will visualize the duration of
a green interval, the length of a queue, or the delay experienced by vehicles traveling through a signalized
intersection with the phasing and timing plan that you design. And you will use this information to
make judgments about the quality of intersection performance, and whether you need to make further
adjustments to the signal timing to improve intersection operations. It is almost as good as standing out
at an intersection, with one eye on the traffic and the other on what is happening in the controller cabinet.
When you have completed the activities in this chapter, you will be able to
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Describe the common categories of transportation models and their attributes
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Describe the characteristics of a microscopic simulation model
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Contrast the performance measures produced by a simulation model
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Describe the categories of traffic analysis tools that are commonly used by a transportation engineer
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Describe the application of a simulation model
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Describe the basic features of VISSIM
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Build and use a simulation model network
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Describe the categories of traffic models
This chapter begins with a Reading (Activity #25) on microsimulation models. Three activities follow,
including an assessment testing you on some of the basic elements of simulation models (Activity #26), an
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The Simulation Environment:
Learning to See a Traffic Signal System