Comparative study of operational performance between roundabout and signalized intersection in addis ababa city: a case study at ayer-tena and gergi-imperial intersections

Abstract

Intersection plays a significant role in the road network, where traffic flowing in different directions crosses each other. Traffic signals and roundabouts controls are commonly used in several at-grade junctions in urban areas for maximizing traffic efficiency and safety by separating traffic movements in time. The intersection performance measures (capacity, a degree of saturation, delay, queue length, fuel consumption, operating costs and emission, etc.) used to compare the intersection performance. In Addis Ababa, most of the intersections are congested and excessive delay during peak hours in the morning and afternoon experienced by the travelers. The objective of this research was to assess and provide a comparative study of operational performance between a roundabout and signalized intersection at the selected intersections. In pursuing the objective of the research study, it focused on two areas Gergi-Imperial Signalized intersection and Ayer-Tena Roundabout. The traffic data on all approach of the intersections were collected by video camera during the most congested days of the week (i.e. Monday, Wednesday and Friday). The traffic volume obtained in different classes of a vehicle has been converted to uniform vehicle fleet by the passenger car equivalency factor. While, the geometric data’s for the selected intersections were measured. Data analysis and processing were performed using SIDRA (Signalized and Unsignalized intersection Design and Research Aid) intersection software to know the traffic flow condition at the intersection. The performance measures used to compare the intersections where the Average delay, Degree of saturation and Level of service at each intersection were interpreted. Based on the findings of the research, the performance of signalized intersection compared with that of roundabouts. The capacities of the signalized intersection were found to be higher than the capacities of roundabout while the Average delay and Degree of saturation for the roundabout was considered to be greater than that of signalized intersections. However, both roundabout and signalized intersection were found to be operating at the same level of service. There was a 13.68% and 31.49 % decrease in the Average delay and Degree of saturation respectively and capacity value increased with 11.18%, after the installation of the proposed signalized intersection at Ayer-Tena intersection. And also, Gergi-Imperial intersection there was a 22.28% and 36.09% decrease in the Average delay and Degree of saturation respectively and capacity value increased with 3.00%, after the installation of the signalized intersection. Therefore, Ayer-Tena and Gergi-Imperial signalized intersections were better than the roundabout in terms of the degree of operational performance. Lastly, Capacity improvement methods such as improving the capacity of roads, improving public transport and avoid effect of pedestrian conflict with vehicles are the major recommendations forwarded.