CAPACITY ANALYSIS OF ROUNDABOUT JUNCTION AND ALTERNATIVE MEASURES UNDER MIXED TRAFFIC FLOW CONDITIONS: A CASE STUDY IN ADDIS ABABA CITY

Abstract

ABSTRACT Mixed traffic prevails in Ethiopian roadways, particularly in urban area like Addis Ababa. In mixed traffic condition the road width is shared by all types of vehicles and capacity of roundabout is described by vehicle type and driver characteristic. Rapid urbanization with economic growth results in a large volume of traffic during the peak hours in most of Addis Ababa city. Increasing traffic volumes is the major problem mentioned in this research. The main emphasis of this study is to analyze the capacity of roundabout and proposing alternative measure under mixed traffic condition. In order to achieve the specific and general objectives traffic volume data, geometric and other important data were collected from selected Roundabout. In the present study the capacity of roundabout is determined by different capacity model such as highway capacity manual (HCM 2010), Indian roads congress (IRC) and SIDRA methods. IRC methods give the capacity of circulating width which highly different from capacity of approaching leg. The HCM model give results close to that of field entry capacity model but sidra is easily calibrated for local condition. Having the concept of those models regression analysis was used to develop roundabout entry capacity model for selected Roundabout. The result of capacity analysis by different capacity models indicates that degrees of saturation of all roundabouts are greater than 1 which poor level of service “F” thus all roundabout are under critical condition. Therefore Erection of traffic signal, constructing additional lane, diverting Buses and tracks to other routes are proposed as alternative measures and performance evaluation after alternative measure were carried out for the selected site