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.
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