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Federal Highway Administration Research and Technology
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Interactive Highway Safety Design Model (IHSDM): Traffic Analysis Module


The image shows a two-lane rural highway in mountainous terrain. There are three vehicles on the right side of the road, driving away from the point of view of the photograph, and three vehicles driving on the left side of the road, driving toward the point of view of the photograph.The Traffic Analysis Module uses the TWOPAS traffic simulation model to estimate traffic quality-of-service measures for an existing or proposed design under current or projected future traffic flows. The traffic analysis module facilitates use of TWOPAS by feeding it the roadway geometry data stored by IHSDM.

TWOPAS is the microscopic traffic simulation model used to develop the two-lane highway chapter of the Transportation Research Board’s (TRB) “Highway Capacity Manual.” TWOPAS produces measures including average speed and percentage of time spent following other vehicles. TWOPAS has the capability to simulate any combination of grades, curves, sight restrictions, no passing zones, and passing and climbing lanes.

The Traffic Analysis Module is particularly useful during project scoping and preliminary engineering for evaluating the operational performance of alternatives to two-lane cross sections, including passing lanes, climbing lanes, and short four-lane sections.

See IHSDM Library for References.


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