The effect of heavy vehicle composition on design traffic loading calculations (E80S)

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. The composition of heavy vehicle traffic has changed dramatically on most of the major roads in southern Africa over the past 10 to 15 years. Observations in various countries confirmed that a continues shift is taken place in the composition of heavy vehicle traffic, which inter alia, leads to an increase in the growth in E80s per heavy vehicles (E80s/HV), the average calculated E80s/HV and subsequently the total calculated E80s. Available data has shown that there is a continues shift in composition from 2 and 3 axle’s heavy vehicles to the larger 4 to 7 axle’s heavy vehicle types. This can, inter alia, be explained by improved vehicle technology, economic growth as well as changes in legalisation (1996), which allows heavier loads to be carried, and better utilisation of heavy vehicles with an increase in economic activity. Cognizance is to be taken of these changes and the effect thereof needs to be incorporated into design traffic loading calculations. The objectives of this paper is to illustrate the changes that are taking place, to show how to incorporate these changes into design calculations and to present a technique, taking the changes in the heavy vehicle composition into consideration, that should be applied in the calculation of design traffic loading.