The relationship between components of vehicle operating costs (VOCs) and highway characteristics has been studied by many researchers over the years, but many issues still remain to be resolved. In particular, although fuel consumption should be the easiest component to model, there is considerable variance between reported results. A comprehensive experiment was therefore designed to investigate the effects of road-surface characteristics on fuel consumption, as a first step toward establishing reliable VOC relations for South African conditions. A passenger car, two medium-sized trucks, and two buses were chosen for coast-down tests to determine rolling resistance over a series of road sections, covering the ranges of surface conditions encountered locally. The models developed predict that at constant speeds on level roads, road-surface characteristics can affect the fuel consumption of passenger cars by up to 7% and that of trucks and buses by up to 20%. It is believed that these models can be applied with confidence in practice, considering the comprehensive nature of the experiment.