Comparison Of Alternative Junction Designs For Light Rail Transit Grade Crossings

Light rail transit is a relatively new mode of transport for Ethiopia. Hence, rigorous researchrnneeds to be done in order to identify and work out flaws in the system. Most of the road-railrnintersections within Addis Ababa LRT corridors are built as grade separated intersections.rnHowever, certain intersections such as Sealite Mehret and CMC roundabout meet the LRTrnline at grade. Research done up to now on these areas, points out significant problems withrnrespect to traffic congestion. The main causes of congestion in this area that are related to thernLRT line are: frequent LRT crossing and interruption of traffic flow, high pedestrian volumesrnat stations near the roundabouts that impede entry and exit flows, lack of U turn areas alongrnthe LRT corridor, which transfers high volumes of U turning vehicles to the roundabouts,rnwhich in turn adds to congestion of the roundabouts. Performance evaluation of thernroundabouts under current traffic conditions was done during peak and off – peak periods.rnResults indicate approach delays of over ten minutes for both locations during peak periods.rnHowever, during off – peak periods the roundabouts perform above level of service C. rnThe goal of this study is to propose alternative solutions to mitigate each cause of congestionrnand to see if adequate performance can be achieved without grade separation at the selectedrnlocations: Sealite Mehret and CMC roundabouts. In order to fulfill this goal necessary datarnwere collected at the study areas. Then the alternatives were designed and modeled usingrnVISSIM simulation software. rnThe alternatives considered are signalized intersection, signalized roundabout, installation ofrnpedestrian signals and diverting U turns to other locations. Comparing these alternativesrnbased on queue length, travel time, intersection delay and level of service under currentrntraffic conditions, showed that the best alternatives for both locations are signalizedrnroundabout and signalized intersection. rnUp on comparing signalized roundabout and signalized intersection alternatives underrnforecasted traffic conditions, analysis results showed that both options have similar travelrntimes and delay. Both alternatives are viable options. However, since signalized roundaboutrnalternative provides the option of functioning as a normal roundabout during off peakrnperiods, and reduces risk of right angle crashes, signalized roundabout is preferred.

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