DEVELOPMENT OF NOMOGRAMS FOR PCU ON URBAN ROADS

Abstract

Due to modernisation in the technology and requirement of - people, different classes of vehicles have emerged. • The mixed traffic flow characteristics are very complex when compared to hOmogeneous traffic which consists of passenger cars only. It is rather difficult to estimate the traffic volume and capacity of roadway facilities under mixed traffic flow unless different vehicle classes are converted to one common standard vehicle unit. It is a common practice to consider the passenger car as the standard vehicle and therefore, all vehicles in the traffic stream other than car are assigned an equivalency factor to convert heterogeneous traffic stream into an homogeneous equivalent. This equivalency factor is called Passenger Car Unit (PCU). Various agencies in India like Central Road Research Institute (CRRI), Indian Road Congress (IRC) have recommended PCU values for different categories of vehicles, which are static and must have been derived for assumed conditions of traffic and roadway. It has been indicated in literature that PCU value is not static but depends on various factors. In the present study, an attempt has been made to establish dynamic nature of PCU. Data collected at mid stock sections in Delhi have been analysed and the variation in PCU with parameter like composition, volume and road width has been explained graphically. Mathematical models relating PCU for a vehicle type and traffic stream characteristics have also been developed. The coefficients in these models were found to be dependent on road width, Number and type of vehicle categories in the traffic stream and other environmental conditions at site. To neutralise the (ii) effect of road width on PCU the data from various sections were converted in per lane width basis and combined. These data were then analysed by changing the number and type of vehicles categories in traffic stream. Finally, nomograms have been developed to evaluate PCU values of a vehicle type under given conditions of traffic and roadway. It is recommended that further study should be carried out by collecting the data in other cities also and by including more numberof vehicle categories in the analysis to make the results geographically transferable.