Capacity Evaluation Of Roundabout Junctions In Addis Ababa

This thesis addresses the most important element of operational performance ofrnroundabout traffic intersections in Addis Ababa: capacity analysis. The relation betweenrna roundabout performance measure and capacity is often expressed in terms of degreernof saturation (Demand volume – Capacity ratio).rnThe capacity analysis is done based on empirical gap – acceptance method that isrnadopted by aaSIDRA software. The necessary geometric data for the analysis (averagernentry width, circulatory road width, number of entry and circulatory lanes, and islandrndiameter), traffic movement data with vehicle characteristics and pedestrians volumernwere collected from 10 roundabouts. These 10 roundabouts represent different sizes ofrninscribed circle diameters of roundabouts, which are directly related to their approachrnleg numbers (3 leg, 4 legs, 5 legs and 6 legs).rnaaSIDRA software capacity analysis results indicated that out of 10 roundabouts 6 ofrnthem have greater than 0.85 degree of saturation. This 0.85 value is recommended byrnanalysis procedure of some model countries such as Australia, Germany, UnitedrnKingdom and U.S.A. Whose roundabouts are designed to operate at no more than 85rnpercents of their estimated capacity.rnApproach entry capacity has been analyzed for all 10 roundabouts at their legs and withrncurve –fitting techniques. Effective capacity verses geometric parameters relationshiprnhave been developed in order to find out the causes of their over Saturation (v/c ratiorngreater than 0.85) And the result indicates; number of entry lanes, number of circulatoryrnlanes, high traffic flow and pedestrian volumes are the major causes of their overrnsaturation.rnFurthermore, The chart is developed using the parameters number of entry lanes,rnnumber of circulatory lanes and opposing circulatory flows, which can assist inrndesigning of roundabouts and forecasting their capacity

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