Passenger car equivalents are used in highway capacity analysis procedures to convert mixed traffic stream volumes into equivalent passenger car volumes. In this paper, a new empirical method for estimating passenger car equivalents for heavy vehicles on freeways is presented. The proposed approach is based on the concept of stochastic capacities. Capacity distribution functions are estimated in passenger car units. By determining the equivalency factor for which the coefficient of variation of the capacity distribution function becomes minimal, passenger car equivalents for heavy vehicles can be derived. The whole methodology is demonstrated for a number of German freeways. The new approach also gives an insight into the extent to which the variance of freeway traffic breakdown volumes is attributed to variable percentages of heavy vehicles.
Samenvatting