Uncertainties in Forecasting: The Role of Strategic Modeling to Control Them

The growing concern about environmental depredations from transport activity at short-range and long-range horizon calls for policies aiming at reorientation of travel demand trends. However every transport policy is subject to risks, environmental or financial ones, and has often long-range effects. This explains the renewed interest in tools which allow detection of these risks and their consequences. There is however a methodological challenge in the elaboration of these simulation tools because we have to take into account many different uncertainties.This paper analyzes the uncertainties associated with transport forecasts using a strategic model recently developed for Lyon's conurbation. Different sources of error and uncertainly are tested and compared by means of the model. It is argued that a strategy of systematic exploration of uncertainly is the preferred way to cope with it and to detect long-term risks associated with transport policy.