Thesis Open Access

Optimization Geometric Design of Roundabout A Case study on Goro Roundabout

Samuel Tezera

Thesis supervisor(s)

Melaku Sisay ( PhD )

Nowadays Addis Ababa city is experiencing rapid growth both in business and construction which increases the number of vehicles and leads to congestion in the city. Thus, currently, there is an attempt to develop infrastructures like road networks improvement and evaluation and improving intersection control mechanisms in the city. But still, there is a huge gap in the developing road segment and the intersection with good operational and safety performance. Therefore it is better to focus on the optimization geometry of roundabout. Many roundabouts in this city are changed to other types of an intersection without a detailed study is conducted. Though, in this study, the Goro roundabout is selected as a case study and was modeled using VISSIM microsimulation software for the process of optimizing the geometry for better operational performance and safety. Also, this software was used to evaluate the performance evaluation of the existing roundabout. In addition to Geometry data, traffic Volume and the pedestrian count is used to conduct the optimization process. Traffic data was collected in morning and night peak hours for three consecutive days from 8:00 am to 9:00 am and from 5:30 pm to 6:30 pm for night peak hour. Pedestrian volume count was used from secondary data of the previous study on each approach that cross the road on both directions in-bound and out-bound to the approach. Then both existing and optimized roundabout operational performance analysis is conducted using VISSIM software. The results showed that of 114.22sec average control delay and 132.58m maximum queue length from the Jackcross approach with “F” LOS. But after optimizing the geometry of the roundabout the performance and capacity of the roundabout are improved and become better in comparison to the previous result with 23.17sec average control delay and 44.1m maximum queue from Jackcross approach with “C” LOS. Therefore, this optimization process increased the performance and capacity of roundabout only through adjusting the geometric elements of roundabout according to provides roundabout guidelines and it is an alternative solution before changing the roundabout to another type of intersections.

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