A software tool approach to re-evaluating superelevation in relation to drainage requirements and vehicle dynamics – a case study

Abstract

Paper presented at the 31st Annual Southern African Transport Conference 9-12 July 2012 "Getting Southern Africa to Work", CSIR International Convention Centre, Pretoria, South Africa.

There is a growing public demand for safer streets and highways. Designing safer roads requires a need to review and improve the existing design guidelines. Road widening and general roadway rehabilitation projects are designed according to the existing roadway conditions. As a result, drainage problems associated with superelevation are prevalent. An evaluation of design alternatives in terms of safety, taking into consideration the superelevation values in relation to the drainage requirements and vehicle dynamics, will prolong the design process. However, it is believed that the additional time invested will result in safer roads and a reduction in vehicular accidents and in addition a potential in lower construction costs. This latter benefit is derived by limiting instances where a design component is overdesigned. The objectives of this paper is to (1) develop drainage criteria for flow paths and depths on road surfaces due to superelevation, (2) analyse the speed and vehicle dynamics at sharp or reduced horizontal curves, (3) develop superelevation criteria for steep longitudinal grades on sharp horizontal curves by identifying and analyzing associated drainage problems and (4) present the outcomes of an independent software tool to assist geometric designers and authorities in the civil engineering industry to design ‘safe’ roads from a geometric design viewpoint by taking factors such as time, cost, quality and context-sensitive design solutions into consideration. The paper draws from an innovative desktop literature analysis study and presents an overview of the research objectives. The desktop study is complemented by the analyses of data from user and stakeholder samples conducted on a section identified on National Route 3. Various physical and theoretical methods of analysis are described in the paper and the ultimate observations and findings will be published in a geometric design manual. The software tool simulates the stormwater drainage flow path in relation to the design superelevation criteria values assessed and evaluated to prevent hydroplaning. The resulting outputs will present a theoretical review of the geometric design considerations involved. The South African Minister of Transport reiterated that we need to prevent the number of accidents on our roads and this paper seeks to persuasively identify a solution from a geometric design perspective. We need to design safer roads.