Issues with the operational analysis of urban intersections

Abstract

Paper presented at the 23rd Annual Southern African Transport Conference 12 - 15 July 2004 "Getting recognition for the importance of transport", CSIR International Convention Centre, Pretoria, South Africa. Operational analyses of urban intersections are often undertaken during traffic impact studies to evaluate the impact of a development on traffic flow. Many improvements to the urban street network are often warranted on the basis of such analyses. Various studies have, however, been undertaken in South Africa and Australia that show that the operational analysis of an intersection is a complex exercise which often produces invalid results. The studies have shown that a large number of factors need to be taken into account when modelling urban intersections, and that the models should be properly calibrated and validated. Unless these issues are properly addressed, the operational analysis of intersections serves little or no purpose. In this paper, it is proposed that simpler approaches should be utilised for the purposes of traffic impact studies. One relative simple approach that can be considered is to evaluate intersections simply in terms of volume/capacity ratios. Improvements to the street network can then be warranted on the basis of such ratios. Maximum ratios for such purpose are proposed in the paper.