A lot of studies have been done to decongest urban road networks especially at major intersections mainly to improve flow efficiency and capacity. Both simulation and computer aided geometric modeling techniques have facilitated these investigations, but little has been done to document the steps leading to the selection of the most optimized architectural configuration of the interchange for implementation. This paper presents the explanation of the steps followed during the decongestion design process of the “GSU” interchange located at the intersection of Nairobi-Thika Super Highway and the newly improved Outer Ring Road (ORR); two key arterial road corridors in Nairobi city, Kenya. The new “GSU” interchange design deployed both micro-simulation modeling using Parallel Microscopic Simulation Software (PARAMICS) and AutoCAD Civil 3D geometric modeling techniques. Using excerpts from the traffic engineering expert’s micro-simulation work together with the design report prepared by the ORR improvement supervision consultant’s team, this paper outlines the workflow steps that led to the final choice of the interchange configuration’s shape and form. The finding of this paper demonstrates the efficacy of the use of micro-simulation models in supporting CAD geometric remodeling of existing intersections for enhanced capacity and flow. The process involving the integration of simulation and geometric modeling is rather complex in nature as it requires team members to exercise patience with each other. This paper recommends that urban road authorities should have a dedicated traffic flow simulation team to work closely with road design engineers in city road network decongestion plans.

decongestion, geometric, modeling