Evaluation of the Effectiveness of Road Underpass on the Traffic Flow: A Case Study at Wellosefer Intersection in Addis Ababa City

Abstract

Urban cities introduced several remedies to decongest traffic and to reduce the severity of accidents, such as providing traffic signals at the intersecting roads at different levels, or grade separating the traffic movement towards different directions. One type of grade separation is Road Underpass. Construction of Road Underpass poses some doubts whether it is effective or not effective on the point of views of the addis ababa traffic management bure. It is for this reason that this study sought to evaluate the effectiveness of Road Underpass structure on traffic flow at the major intersection in the case of Wellosefer intersection in Addis Ababa. The data needed in this study are primary and secondary data. The primary data are the existing traffic volume recorded between 7:00 AM – 6:00 PM from Monday to Friday. While the secondary data obtained from the Consulting Office of the Project "before" the improvement of Wellosefer intersection and the previous study. From these data, the analysis provided results on vehicle travel time and delay for a case “before" and “after" improvement of a Road Underpass structure to serve as the measure for evaluation. The analysis was supplemented by SIDRA Software. Based on the findings of the study, a case "Before" Improvement of Wellosefer UnSignalized T-Intersection indicated with an average delay of vehicles of about 535.7 seconds, while the travel time of vehicles of about 574.7 seconds. On the other hand, a case "After" Improvement of Wellosefer intersection considering Signalized TIntersection, Roundabout only, and Road Underpass with Roundabout at the upper level, the Signalized T-intersection showed an average delay and travel time of 344.3 seconds and 365.0 seconds, respectively. From this result, there was a 15.4% reduction in average delay when signalized intersection had been implemented . Likewise, for Road Underpass with Roundabout at the upper level, the results revealed that there was a significant reduction in average delay of vehicles of about 42 % from Un-Signalized TIntersection. Comparing this result with the Signalized intersection using the same traffic data, it indicated that there was a significant decrease in average delay. Extending the analysis for the case of Roundabout only considering the same traffic data at present condition. The results showed motorists and commuters could be experiencing an average delay of about 355.8 seconds and avergae travel time of 390.0 seconds. Therefore, the results of these findings of the study by comparing the different intersection design alternatives, a combination of Road Underpass and Roundabout at the upper level as in the case of Wellosefer intersection, is the most effective alternative. In addition, the results clarified some doubts of whether effective or not effective. However, to eliminate future traffic malady at the major intersections in Addis Ababa, a long-term solution is recommended such as construction of Road Underpass structure or flyover structure with Roundabout or Traffic signal lights at ground level, but subject to some constraints which requires proper integration of other factors affecting traffic flow within the entire road network.