PREDICTING ROAD USER COSTS FOR HIGHWAY INVESTMENT DECISIONS

Prior to 1970 information on road user costs in less developed countries was scanty but during the last decade four major studies have collected and analysed information on road user costs. These four studies provide highway planners with substantial new information. The Transport and Road Research Laboratory (UK) have studied road user costs in Kenya and the Caribbean and more recently studies have been performed in Brazil (by the Brazilian Ministry of Transport and the United Nations Development Program and in India (by the Central Road Research Institute, New Delhi). All these studies have produced equations to predict elements of road user costs as functions of highway characteristics. This paper concerns the interpretation of these studies' results and the uses to which they can be put. The first section of the paper briefly describes the role of road user costs in highway planning and reviews the four studies. In the second sections we address the problem of estimating road user cost equations. Since the data available are generally not experimentally generated this is a non-trivial issue. An important consideration here is whether transport companies of different efficiencies are evenly distributed over highways of different qualities. The third section presents some results from the studies and examines their interpretation. In particular we examine the distinction between long run and short run cost relationships. In the short run operators do not adjust fleet composition when highway conditions change: in the long run they may. The final section contains concluding remarks. (Author/TRRL)