EFFECT OF TRAFFIC MIX, VOLUME, AND GEOMETRICS ON THE TRIP TIME OF PASSENGER CARS AND TRUCKS ON URBAN FREEWAYS

The objective of this paper is to investigate and quantify the relation between the average travel time per unit distance experienced by passenger cars, trucks, and other vehicles and the prevailing volumes of passenger cars and trucks on urban freeway sections. This macroscopic relation is examined for freeway sections exhibiting four types of geometric and operational characteristics (pipe, diverge, merge, and weave sections). The models are calibrated for each type of section using the FHWA 1982 data set on urban truck freeway characteristics, thereby providing the basis for the systematic testing of (a) the effect of geometrics on the relative effects of passenger cars and trucks on freeway performance, and (b) the relative sensitivity of the service quality experienced by passenger cars and trucks to the components of the traffic stream. These questions are of current practical interest to agencies contemplating truck-related highway improvements. The results indicate that the coefficients of the respective volume components vary significantly across section types, yielding volume effect truck passenger car equivalents (pces), in terms of impact on average travel time, which differ markedly from one type to another. This suggests that the undifferentiated treatment of pces for certain geometric and operational conditions may not be appropriate.