CAPACITY OF URBAN ROADS USING AREAL DENSITY CONCEPT

Abstract

Capacity determination from speed-flow curve require knowledge of passenger car units (PCU) for different types of vehilces in the traffic stream. PCU for a vehicle type has been the subject of continuing research for last 3 decades. There exists large variation in PCU values being adopted in different parts of the world. At national level also, different organisations have suggested different PCU values for the same type of vehicle. The concept of PCU is very crucial in the analysis of traffic flow. Any bias in these values will lead to bias in capacity estimation. Morever, the terms like traffic density and traffic flow in their conventional forms remain no longer valid for traffic conditions prevailing in India and other developing countries. These terms have been replaced by areal density and areal density flow in the present study to suit the mixed traffic conditions. These parameters consider the longitudinal and lateral placement of vehicles and therefore are more logical. Data collected through videography at a few mid block sections of Delhi have been analysed to establish the speed-areal density relationships. Capacity of the section was determined using the flow maximisation technique and it has been shown that the capacity values obtained from areal density concept closely match with the values given in IRC:106-1990. The approach however, is certainly better than the conventional one in the sense that it does not require PCU values of individual vehicles and yet the capacity values is obtained in terms of PCU/hr.