Vehicle Speeds and Operating Costs

Book excerpt: Road-user costs are the largest cost elements in road transport. Improvements in road conditions can yet pay substantial dividends by reducing vehicle operating costs. Expressing vehicle operating costs in relation to road characteristics--geometry and pavement condition--is the logical approach. For certain cost components, especially fuel consumption, the required data can be obtained by controlled experiments. Vehicle maintenance costs utilizing extensive road-user surveys are needed. This volume takes an aggregate-mechanistic view of vehicle speed and operating costs under free flow conditions. Basing their analysis on the mechanistic principles of propulsion and motion as well as on postulated assumptions of driver behavior, the authors arrive at predictions at three levels of detail, ranging from a simulation method for use in detailed geometric design at the link level to an aggregate method for use in investment planning at the sectoral level. The models were estimated using the comprehensive database collected in the Brazil-UNDP-World Bank highway research project and were validated along with data sets from India. One of the significant contributions to highway economics research made in this study is the probabilistic limiting velocity approach to steady-state speed prediction, which, combined with the aggregate-mechanistic methodology, will provide a possible basis for future research on the far more complex problem of operating costs under congested conditions.