Highway Capacity Manual

The Highway Capacity Manual (HCM) is a publication of the Transportation Research Board of the National Academies of Science in the United States. It contains concepts, guidelines, and computational procedures for computing the capacity and quality of service of various highway facilities, including freeways, highways, arterial roads, roundabouts, signalized and unsignalized intersections, rural highways, and the effects of mass transit, pedestrians, and bicycles on the performance of these systems.

There have been six editions with improved and updated procedures from 1950 to 2016, and two major updates to the HCM 1985 edition, in 1994, 1997 and 2015. The HCM has been a worldwide reference for transportation and traffic engineering scholars and practitioners, and also the base of several country specific capacity manuals. The current version, the Highway Capacity Manual, Sixth Edition: A Guide for Multimodal Mobility Analysis, or HCM 2016, or HCM6, was released in October 2016 The sixth edition incorporates the latest research on highway capacity, quality of service, active traffic and demand management, and travel time reliability.

There are more than six decades of research behind the HCM. The first edition of the Highway Capacity Manual was released in 1950 and contained 147 pages broken apart into eight parts. It was the result of a collaborative effort between the Transportation Research Board (TRB) and the Bureau of Public Roads, predecessor to the Federal Highway Administration.

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