Review of Methods for Estimation of Passenger Car Unit Values of Vehicles

Estimation of passenger car unit (PCU) values is very important for traffic capacity analysis and other relevant applications such as level of service (LOS) measures, determination of saturation flow rate, signal design and coordination, and development of traffic flow models. Because of such wide applications, the accuracy of PCU values is highly significant in traffic flow analysis. Many research works have been carried out on estimation of PCUs in the past few decades. In developed countries, various methods were developed for estimating PCU values for different types of facilities which carry trucks and buses of lesser composition. But these methods are not completely analogous for mixed traffic due to the presence of wide variety of vehicle types, nonlane discipline, intraclass variability of vehicles and their maneuverability. With this consideration, various methods used for estimating PCUs for different facility types under homogeneous and mixed traffic conditions are reviewed and the drawbacks of the existing methods are identified in this paper. The challenges in estimating PCU values and future directions for improving the PCU estimation methods are also presented.