Highly congested roundabouts are usually considered as the critical points within the urban road network and the evaluation of their performance provides valuable understanding and useful indication about the performance of the city road network system. Roundabouts should be designed to operate at no more than 85 percent of their estimated capacity. Beyond this threshold, delay and queues vary significantly from their mean values. The roundabout approach is dependent on the conflicting circulating flow and the roundabout’s geometric elements. In Addis Ababa, most of the intersections are congested and operate in poor LOS. During peak hours, it is common to see congestion, long queues, and delay at junctions. Accordingly, the objective of the study was to evaluate the operational characteristics of the selected roundabout in Addis Ababa. This research focused on the capacity and evaluation of the level of service at Gerji Imperial Roundabout and addressed the most important element of operational characteristics. The methodology employed for this study was the quantitative descriptive research design method. The necessary geometric data for the analysis (average entry width, circulatory road width, number of entry and circulatory lanes, and island diameter), traffic movement data with vehicle characteristics, and pedestrian volume were collected from the study area. The capacity analysis was done based on the gap – acceptance method that is adopted by the SIDRA Software program. Based on the results, the degree of congestion of the roundabout found out to have 1.749 which is far beyond the recommended values for a satisfactory level of service. Therefore, this indicates that the Gerji-Imperial roundabout is serving in a poor level of service. It is recommended to construct a road overpass or underpass at the most problematic approach to improve the operational capacity of the intersection.
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Published on 01/01/2017
Licence: CC BY-NC-SA license
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