EVALUATION OF CAPACITY OF ROUNDABOUTS USING ANALYTICAL MODEL IN MIXED TRAFFIC FLOW CONDITIONS

Abstract

Capacity is the main determinant of analysing the traffic performance of roundabouts. The movements of the vehicles were observed at 2 roundabouts in Varanasi. Gap acceptance and follow up time were estimated for cars for one hour analysis. The relation between a roundabout performance measure and capacity is expressed in terms of degree of saturation (volume – Capacity ratio). The capacity analysis is done based on gap acceptance method that is adopted by Tanner based on the HCM 2010. The traffic movement data with vehicle characteristics were collected from 2 roundabouts in Varanasi. These 2 roundabouts are directly related to their approach leg numbers.Approach entry capacity has been analysed for all 2 roundabouts at their legs. Effective capacity verses entry flow relationship have been developed in order to find out the causes of their over Saturation (v/c ratio greater than 0.85) And the result indicates; number of entry lanes, number of circulatory lanes and high traffic flow are the major causes of their over saturation.