Role of travel demand models in appraisal and policy-making

The purpose of this paper is to examine the role of travel demand models in the appraisal and policy-making process. The travel demand modelling process is described, with particular emphasis on identifying where policy issues can be examined and possible weaknesses in the methodology. Then the historical development of the models is considered. This is a mixture of policy-making, public pressure, government response, and analytical development. It is shown how the national road-building programme is intimately linked with the process of forecasting the demand for road space. However, the forecasting procedure is pragmatic rather than theoretically sound, and not very accurate. Similar weaknesses are found at a local level. The paper is concluded by consideration of ways of improving the forecasting procedures.