PCU Estimation for Different Vehicle Classes on Highways and Freeways and its variation with traffic parameters

Abstract

Traffic flow is not homogeneous in many parts of the world. There are different vehicle types present in a traffic stream at a time. The traffic stream is usually more heterogenous in developing countries like Pakistan. As the volume and number of vehicle types in a traffic stream increase, their interaction and influence on each other increase. To reduce the complexity of such situations Passenger Car Unit (PCU) is used. This is a commonly used approach to convert this heterogeneous traffic into a homogeneous volume having the same impact. PCU estimation is needed for each of the vehicle types present in a traffic stream to analyze and design the performance of various traffic facilities and to manage the regulation of the traffic stream. This study attempts to determine the PCU factor for highways and freeways in Pakistan. Four locations are selected for the purpose where MetroCount@5600 is installed to collect speed data along with classified traffic counts. Two of the location selected are median-separated four-lane highways, one a two-lane highway section and another a six-lane freeway section. The methods used include Speed methods (Chandra Method, Modified Chandra Method), Headway method, and Equal Density method (EDM) based on simulation techniques. Roads geometric data and vehicle dimensions are obtained from the field. PTV VISSIM which is a micro-simulation software is used for the calculation of density at different volumes at the DCPs. The PCU values estimated by different methods give satisfactory results. The value given by speed methods falls close to each other. PCU values estimated by the Equal Density method are more reliable than all the methods. The PCU factors vary with different factors which include speed, volume, traffic composition, and road class. It is recommended to use other methods for PCU calculation and determine its variability with other parameters like LOS, geometric features of roadways, and pavement condition.