Passenger car equivalents for heavy vehicles at freeways & multilane highways: some critical issues

Abstract

One of the important issues affecting the accuracy of traffic analyses is heterogeneity in the vehicular traffic mix that composes a traffic stream. Typically, the majority of vehicles in a traffic stream are passenger cars or vehicles that are similar to passenger cars in physical characteristics and performance, such as sport utility vehicles, pick-up trucks and minivans. Heavy vehicles, which usually constitute the remaining smaller proportion of a traffic mix, are larger in dimension and often inferior to passenger cars in performance. Heavy vehicles consist mainly of trucks used in freight transportation, larger buses and recreational vehicles. Despite being the smaller proportion of vehicular traffic, heavy vehicles are known for their important impacts on the traffic stream. Historically, the effect of heavy vehicles on traffic flow has been accounted for through the use of passenger car equivalency factors. These factors are intended to approximate the effect of heavy vehicles and are expressed as multiples (of the effect) of an average passenger car. In the United States, the Highway Capacity Manual (HCM) provides passenger car equivalents (PCEs) for use in capacity and level of service (LOS) analyses. Using PCEs, a heterogeneous mix of vehicles in a traffic stream can be expressed in a standardized unit of traffic, such as passenger car. PCEs are considered essential in carrying out most traffic analyses.