Abstract
The highway capacity manual (HCM) is the publication used most often to estimate capacity. Field measurements in previous research have shown that the capacities at several freeway bottlenecks are noticeably lower than the values recommended in the HCM (highway capacity manual), by an order of a few hundred vehicles per lane. In addition, several articles have shown that maximum freeway throughput may differ between undersaturated and oversaturated conditions. This paper assembles capacity flows before and after the initiation of oversaturation, discusses recommended definitions of capacity, and provides capacity values and capacity prediction models for various types of freeway segments. It is recommended to define prebreakdown capacity as the 85th percentile of the 15-min average prebreakdown flow and the postbreakdown capacity as the 85th percentile of the 15-min average discharge flow. A clear drop in throughput between prebreakdown and discharge capacity values was observed. The paper concludes by providing recommended capacity values as a function of the number of lanes and the segment type. These values are significantly lower than those recommended in the HCM (highway capacity manual) for basic freeway segments.
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Acknowledgments
This research was funded by the Florida Department of Transportation through Contract BDV32-977-03. The opinions expressed here are those of the authors and do not necessarily represent the opinions of the Florida DOT.
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Published In
Journal of Transportation Engineering, Part A: Systems
Volume 143 • Issue 3 • March 2017
Copyright
©2016 American Society of Civil Engineers.
History
Received: Mar 9, 2015
Accepted: Sep 26, 2016
Published online: Nov 30, 2016
Published in print: Mar 1, 2017
Discussion open until: Apr 30, 2017
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