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Chapter 2: Modeling What We’ve Observed: Queuing Systems
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The purpose of this activity is to provide a framework for you to think about traffic flow at signalized
intersections, both in a model representation and in connecting this model to what you observe in the field.
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Represent and interpret queue accumulation polygons for a range of traffic flow and control conditions
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Activity #8: “Modeling Traffic Flow at Signalized Intersections”
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Using an Excel spreadsheet, summarize your field observations, including your field notes and the data
that you’ve collected. The spreadsheet should include the following sections, integrating field data and
answers to the questions from Tasks 1 through 4.
Tab 1
: Title page with activity number and title, authors, and date completed
Tab 2:
Summary of your general observations and sketch
Tab 3:
Table 4 data and a description of the sequence of movements that you observed
Tab 4:
Table 5 data and a discussion of the queue pattern that you observed, including a chart of the
queue accumulation polygon that results from your data and a description of how you would
compute total delay using this information
Tab 5:
Table 6 data and a summary of the headway data that you’ve observed. Description of the
efficiency of the intersection timing for the lane that you observed, including an estimate of
the green utilization time and the number of cycle failures. Note that (1) green utilization time
is the ratio of the duration of the green interval during which the queue is clearing to the total
duration of the green interval, and (2) cycle failure occurs when the queue fails to clear during
the green interval.
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Summary of traffic flow problems that you observed
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Phone that records time to the nearest second
These tasks should be completed during both the morning and afternoon peak periods.
Walk or drive to your assigned intersection. Spend 15 minutes observing the operation of the intersection.
Record the physical elements of the intersection, including the intersection geometry, lane striping, the
location of the cabinet and other signal furniture, and other features that you consider to be important.
Prepare a sketch of the intersection and note each of these items on the sketch.
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From Model to the Real World: Field Observations