Design of a Flyover and Roundabout underneath it to ease the Traffic Congestion at the Rajagiriya Junction

Abstract

Urban traffic congestion has become a serious concern of transportation professionals and traffic managers. Rajagiriya town becomes severely congested due to vehicular traffic during daytime. Therefore, efforts were made to quantify this congestion and formulate appropriate measures to mitigate it. Rajagiriya town consists of several intersections located at close proximity to one another, and they have become potential sources of acute traffic congestion. There are three junctions situated along the main road (i.e. Sri-Jayewardenepura road) namely Police station junction, Bo-tree junction and the Kohilawatta road junction. In order to find a solution to this traffic congestion, the capacities of the roads were evaluated by compiling data related to prevailing vehicular flows and collecting other supportive information both as of today and for the next 20 years (i.e. up to the year 2035). From the capacity calculations made from field data it is evident that all the roads in the area would fail to cater to the future traffic demands. Road widths, lanes and walkway shoulders were designed using the U.S. Highway Capacity Manual so as to meet the anticipated traffic demands and pedestrian requirements of the future, {[}1]. As a solution to ease the transportation problems mentioned, initiatives were taken to separate out the traffic flows by constructing a flyover. The design of the flyover was done considering a heavy traffic movement and the flyover was so located that it did not hinder the three junctions. The location for the flyover was decided based on the prevailing operating conditions. For the flyover, pre-stressed material was proposed as it is found to be economical whereas pre-stressed concrete and in-situ concrete were proposed for the beams and piers respectively. Roundabouts were found to be a suitable solution to manage the traffic flow under the flyover. The roundabout design was done using a turning template and based on the Australian Standards (AUSTROADS) {[}2]. The selection and the design of a roundabout, as with any intersection, require the balancing of competing objectives such as safety, operational performance, and accessibility for all users. Factors such as land use, aesthetics, and environmental aspects too were considered. Flexible concepts allow room for independent designs and techniques tailored for a particular situation while emphasizing performance based evaluation of those designs. Finally a suitable layout plan was introduced for the study.