Forecasts in urban transportation planning: Uses,methods, and dilemmas

Legislation and regulation require cities to prepare forecasts of patronage and J. cost when they compete for federal funds with which to build urban rapid transit systems. Experience shows that these forecasts routinely overestimate patronage and underestimate costs. The explanation for this phenomenon is to be found not in technical shortcomings in the forecasting methods, but in the fact that the forecasts are critically dependent on assumptions of key parameters. Assumptions are chosen to produce forecasts which justify projects favored on the basis of local politics. In an environment in which competition for funds is vigorous, effective advocacy becomes more important than objectivity in the use of forecasting methods. This paper reviews forecasting models widely used by transportation consultants, and shows how the models are manipulated in order to promote systems which have been chosen on the basis of political criteria.