A relook at residential trip generation variables

Abstract

Paper presented at the 28th Annual Southern African Transport Conference 6 - 9 July 2009 "Sustainable Transport", CSIR International Convention Centre, Pretoria, South Africa.

Income forms the basis for the differentiation of residential trip generation rates in South Africa. In the last ten to fifteen years this country has experienced sweeping political and socio-economic changes; with the result that income categories as described in the South African Trip Generation Rates (1995) have become difficult to apply. This situation is proving to be a source of frustration and contention for developers, traffic engineers and the local authorities alike. A review of the current trip generation rates as well as the methodology used to establish trip rates is called for. The purpose of the paper is to investigate alternative independent variables to define residential trip generation in middle and higher income areas, and to develop a method that can be applied in practice. Based on the literature and practical experience with traffic impact studies, the following independent variables were selected for investigation:Size of development in number of units.Density of development in units per hectare.Size of units in square meters or number of bedrooms Trip generation surveys were undertaken at 55 locations in Johannesburg and Ekurhuleni. The independent variable that performed the best as a predictor of residential trip rates is Density of development. The weighted average method of establishing trip rates is applied, and appropriate trip rates are provided. Compared to the rates published in the South African Trip Generation Rates (1995) and other relevant sources available in South Africa, average trip rates appear to have declined, necessitating a more in-depth relook at trip generation rates and procedures used in traffic impacts studies.