DETERMINATION. OF EQUIVALENT HOMOGENEOUS TRAFFIC FLOW IN RELATION TO ROADWAY OCCUPANCY

Abstract

To make the capacity-analysis feasible, the normal procedure is to homogeniie the mixed traffic in terms of a common vehicle. For this purpose different types of vehicles having widely varying sizes, 'speeds and manoeuvrability have been expressed in terms of a common design-vehicle-unit, viz., passenger-car. Certain values of passenger-car-equivalency-factors (commonly known as Passenger-Car-Units or PCUs) for different types of vehicles have been suggested by various agencies in India,and abroad too,- based upon the relative speed of vehiclos in the flow, physical dimensions or congestion indices and densities, and overall levels of service. Certain constant values of such equivalency factors can be adopted only tentatively till more rational values, depending upon their relative interference values in a traffic stream under prevailing roadway and traffic conditions, are evaluated. For a given roadway conditions, the prevailing traffic conditions are subject to variations in time-space domain. It clearly brings out that the equivalency factors must be susceptible to changes in traffic conditions and thus, their constant values lose much of their meaning, as the deterministic values do not have a built in corrective mechanism. The study, presented here, suggests an approach to determine passenger-cer-equivalents (PCEs) which are sensitive to traffic conditions on a prevailing croadway. (iv) It considers the traffic flow, as a complex stochastic process. The approach also enables calculation of capacity under prevailing roadway and traffic conditions and hence evaluation of utilization of the roadway. The entire approach has been computerized, for ease of analysis. Analysis has been done for a 2-lane busy—city—street as well as for a 4—lane divided—urban—arterial using actual field data. An attempt has been made to compare PCEs for the two cases and also to study their variation with volume and composition of traffic with the help of generated data for the two--lane flow. Separate computer programw:, have been developed for the two cases, which can readily -be utilized with certain traffic input data ftom the field, for similar roadway conditions. Similar computer programAlw may also be developed for significantly different roadway conditions, e.g., rural roads, intersection approaches, bridge approaches,curved sections etc. Thu; a brief outline of future direction of work has also been incorporated herein, (iv) It considers the traffic flow, as a complex stochastic process. The approach also enables calculation of capacity under prevailing roadway and traffic conditions and hence evaluation of utilization of the roadway. The entire approach has been computerized, for'case of analysis. Analysis has been done for a 2—lane busy—city—street as well as for a 4—lane divided—urban—arterial using actual field data. An attempt has been made to compare PCEs for the two cases and also to study their variation with volume and composition of traffic with the help of generated data for the twc—•lane flow. Separate computer programv., have been developed for the two cases, which can readily be utilized with certain traffic input data from the field, for similar roadway conditions. Similar computer programs may also be developed for significantly different roadway conditions, e.g., rural roads, intersection approaches, bridge approaches, curved sections etc. Thus, a brief outline of future direction of work has also been incorporated