Considerations in Applying the 1985 HCM Procedures

by Charles Manning, Roger Creighton Associates Inc, Delmar, NY, USA,



Document Type: Proceeding Paper

Part of: Microcomputer Applications in Transportation II

Abstract:

The paper examines the impact of critical assumptions in the 1985 Highway Capacity Manual (HCM) procedures on the resulting measures of effectiveness -- volume/capacity ratio, delay, and level of service. Critical assumptions are examined using examples which reflect real world conditions including heavy right and left turns and severely unbalanced flow. The examples are used to illustrate the impact of changing a critical variable. In addition to lane grouping, the sensitivity of results to changes in the following variables will be illustrated: area and signal type designations; permissive/protected left turn considerations; right turn factors on single lane approaches; left turn factors; cycle length and timing considerations. For each variable at least two values will be used in the HCM calculation. Although both variables may appear reasonable after a quick review, they will be shown to produce significantly different results.

Subject Headings: Traffic signals | Traffic capacity | Left turns | Intersections | Driver behavior | Volume measurement | Traffic volume

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