The Highway Capacity Manual (HCM) is a publication of the Transportation Research Board (TRB) 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 five editions with improved and updated procedures from 1950 to 2010, and two major updates to the HCM 1985 edition, in 1994 and 1997.[1] 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.
There are more than five 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).[1]
The following editions were published by the Transportation Research Board in 1965, 1985, 2000 and 2010. The latest edition HCM 2010 is the culmination of a multi-agency effort (including TRB, AASHTO, and FHWA) over many years to meet the changing analytical needs and to provide contemporary evaluation tools. The fifth edition, HCM 2010, has been released and is available from TRB.