Empirical Investigations on Passenger Car Unit for Urban Freeways in Shanghai

Abstract

Heavy vehicles have significant impact on the traffic performance of freeways. The passenger car unit (PCU) is a common measure used for freeway design and analysis. With the availability of a huge amount of empirical traffic data, investigations on the determination of the PCUs are feasible. This paper uses the simple linear density-speed function to estimate the capacities and investigate the relationship between capacities and the percentage of heavy vehicles. Empirical traffic data from five locations from the Outer Ring in Shanghai have been utilized for the analyses. The results show that the PCU value decreases with the rising percentage of heavy vehicles when the percentage of heavy vehicles is larger than 20%. In cases where the percentage of heavy vehicles is smaller than 20%, the PCU could be either increasing or decreasing, and is strongly dependent on the capacity that is estimated when there are no heavy vehicles in the traffic.