To assist with the economic appraisal of road investment and maintenance expenditure the Highway Design and Maintenance Standards Model (RTIM) and the Road Transport Investment Model (RTIM) were developed to estimate changes in transport costs associated with improvements in road condition, such as reduced road roughness. Within developing countries (where passenger time savings are usually ascribed little value) changes in vehicle maintenance costs represent an important component of the benefits of reduced transport costs resulting from improvements in road condition.
In order to improve the modelling of vehicle maintenance costs this report examines field data collected from Botswana, St Helena, and Pakistan and compares the results with HDM and RTIM. Large differences are shown to exist in the vehicle maintenance cost relationships (expressed in terms of parts consumption and maintenance labour input) between the different model formulations and the field data; Pakistan's vehicle maintenance costs are particularly low. A simplified parts consumption model is proposed using three coefficients to relate parts consumption to vehicle age and road roughness. The results from a survey of articulated trucks in Botswana fit the simple model well; two of the coefficients are close to those derived from Brazilian and Indian data used in HDM. However with the other field surveys there is little consistency in the coefficients that are derived.