Driver Population Adjustment Factors for the Highway Capacity Manual Work Zone CapacityEquation

Document Type


Journal/Book Title/Conference

Proceedings of the 2008 Transportation Research Board Annual Meeting


National Academy of Sciences

Publication Date



This paper presents a proposed enhancement to the current methodology for assessing capacity in work zones. Research into the impact of driver behavior in work zone related merge areas has revealed the influence of driver behavior on flow quality when drivers encounter and respond to changing roadway conditions and lane configurations. Research suggests the implementation of a driver familiarity adjustment factor for use in the Highway Capacity Manual work zone capacity equation similar to the factor used in the general highway capacity equation is appropriate. The value of and thereby the influence of the proposed factor is based on assessment of driver familiarity, driver adaptability, driver aggressiveness, and driver accommodation tendencies that are unique demographic groups defined by locality, region, driver experience, and/or driver age. The development of the proposed factor and the underlying concepts are a product of several years of theoretical and field-based traffic flow and human factors research. The principle embodied in the adjustment factor is that the efficiency with which drivers adjust to changing roadway conditions while interacting with other drivers on the roadway directly impacts capacity. Quantifying the adjustment factors and developing the measures associated with the assignment of a value to the adjustment factor have the potential to aid transportation professionals in better estimating the capacity of a freeway work zone and ultimately influence the development of optimal work zone strategies.

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