United States Department of Transportation
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Development of speed models for improving travel forecasting and highway performance evaluation : [technical summary].
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2013-12-01
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By Moses, Ren
[PDF-1.31 MB]
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Abstract:Travel forecasting models predict travel demand based on the present transportation system and its use. Transportation modelers must develop, validate, and calibrate models to ensure that predicted travel demand is as close to reality as possible. Most travel forecasting models require measures of free flow speed and practical capacity, based on evaluations of current highway performance, as well as functions that relate traffic volume to travel time, so-called volume delay functions (VDF), which are very sensitive to free flow speed and practical capacity. Several VDFs have been proposed, including the four examined in this project: the Bureau of Public Roads (BPR) function; the Davidson function; the Conical function; and the Akcelik function. The choice of VDF depends on the nature of the highway to which it is applied, and classifying highways for this purpose and matching them to appropriate models represents a major challenge to modelers.
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