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Sub-problem 5a - Page 1 of 3

ID# C405A01

Sub-problem 5a: Network Simulation

Step 1. Setup

VISSIM is the traffic simulation package we chose to use, so the specific input data files reflect the needs of that software. However, many of these characteristics and inputs would be required for other modeling software as well. A summary of the inputs and assumptions we used is as follows:

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network configuration (highway sections and their connections)

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link distances set to values obtained from the local MPO (Metropolitan Planning Organization) accurate to the nearest 10 feet

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geometrics for all highway segments

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freeway free-flow speed density functions set to a minimum of 50 mph and a maximum of 60 mph

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ramp speed density functions for the loop ramps, etc., set to a minimum of 22 mph and a maximum of 28 mph

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ramp speed density functions for the right-hand ramps and semi-direct ramps set to a minimum of 43 mph and a maximum of 48 mph

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ramp speed density functions for all remaining facilities set to a minimum of 27 mph and a maximum of 35 mph

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trip matrix using locations A through M in Exhibit 4-78 as the origins and destinations

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heavy vehicle percentages set nominally at 5% throughout the network

The O-D trip matrix was obtained from the Capital District Transportation Committee (CDTC), which serves as the local MPO. The matrix is derived from the outputs of the travel forecasting model that CDTC uses in all of its planning studies. Since it is generated data rather than observed volumes, we do not expect exact matches between the traffic volumes observed in the field and those predicted by the O-D trip matrix. The traffic volume on a given link in a given time period predicted by the O-D trip matrix may be different from the value that was actually observed in the field. The difference is that the predicted value uses a routing algorithm to assign flows to network paths that might not be consistent with the way drivers choose routes.

Consider:

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What type of output or measures of effectiveness might we expect to obtain from simulation models that would provide value above and beyond using HCM methodologies?

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How does a simulation model help develop engineering solutions?

Discussion:
Take a few minutes to consider these questions. Click continue when you are ready to proceed.

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