Not everyone is convinced that the large-scale infrastructure investments, planned in the context of the Trans-European Networks (TENs) of the European Union (EU), will give rise to their intended benefits. In particular, it is necessary to estimate reliably how much induced traffic these investments will bring, so that environmental impacts can be assessed properly as part of the decision process for each investment. It is essential to define `induced traffic', and design a framework that makes such a definition operational in modelling terms. A functionally consistent definition, though not a behaviourally consistent definition, can be achieved across all studies. Transport modelling needs must be separated from subsequent evaluation needs. Whereas travel demand models quantify the effects of infrastructure improvements, the evaluation must translate them into impacts by combining and weighting them according to the project's objectives. This paper gives examples of the evidence of induced traffic on major infrastructures, discusses the modelling of induced traffic, and considers some issues in determining suitable approaches. It was found that the forecasting of induced traffic on new transport infrastructure cannot be separated from the procedures used for estimating all other demand effects.
Abstract