Capacity and Level-of-Service Concepts in the Highway Capacity Manual

T he 1985 Highway Capacity Man-ua / (HCM) represents a signifi-cant change in many of the com-putational procedures employed to evaluate highway capacity and opera-tion. ’ Flowing from over 15 years of com-prehensive research and development involving numerous research agencies, research sponsors, and individual mem-bers of the Transportation Research Board’s Committee on Highway Capac-ity and Quality of Service, the new man-ual updates not only computational pro-cedures, but some of the basic concepts involved in highway capacity analysis as well. This article discusses the two con