The Measurement of Urban Travel Demand

It is a truism that the transportation system is a critical component of every urban economy, and that transportation policy decisions can have a profound effect on the development of the urban system. Public transportation projects are often massive and mutually exclusive, with irreversible cumulative effects over long periods. If major social losses are to be avoided, careful planning based on a conceptually sound and empirically accurate benefit-cost calculus is essential. Accurate forecasts of travel demand under alternative transport policies are required for precise calculations of benefits. To be fully satisfactory, these forecasts must be sufficiently sensitive to reflect the impact of the changing urban environment over the lifetime of proposed transport projects. Travel demand forecasting has long been the province of transportation engineers, who have built up over the years considerable empirical wisdom and a repertory of largely ad hoc models which have proved successful in various applications. The contribution of psychologists and economists to forecasting methodology has been limited; despite a surge of recent interest, there still does not exist a solid foundation in behavioral theory for demand forecasting