Conceptual Approach for Estimating Dynamic Passenger Car Units on Urban Arterial Roads by Using Simultaneous Equations

Abstract

This study demonstrates that passenger car unit (PCU) values for a vehicle are not static and vary with traffic volume and composition. Data collected at eight urban arterial roads in India were analyzed to explain the dynamic nature of the PCU factor. All vehicles in the traffic stream were divided into five categories, and simultaneous equations were developed to determine the speed of a vehicle type from information on traffic volume and composition. These equations were used to show the variation in PCU values with traffic volume and composition on a road. The change in PCU values was explained on the basis of the relative interaction of vehicle type in the traffic stream at different volume levels. A proposed range of PCU values for big vehicles was from 1.47 to 1.65 for big cars and for heavy vehicles from 5.51 to 6.54, respectively, when their proportions in the mix remained within an observed range in the field. Similarly, a range of PCU values for motorized three-wheelers of 0.99 to 1.01 and a set of PCU values for motorized two-wheelers of 0.20 to 0.23 were obtained. Accuracy of the PCU values estimated through simultaneous equations was checked by comparing the estimated values with those calculated directly from the field data. Statistical testing showed that there was no significant difference between field-estimated and model-predicted PCU values. Further, the speed–volume relationships developed by using two sets of PCU factors yielded the capacity values with a difference of less than 2%; this result indicates the correctness of the methodology in this study.