Chapter 12: Models in Policy and Policy in Models: Integrating Decision Making^*

Transport models have always been designed with an emphasis on guiding policy decisions. Early models were more concerned with forecasting the implications of adopting alternative policy details than with the evaluation of alternative policy scenarios. The main objective has been to tackle the main problems of transport: issues such as congestion, environmental impact and the efficient provision of public transport. But the early use of models was largely within the “predict and provide” paradigm, in which the main purpose was to assess the best possible investment policy to provide the capacity necessary to meet forecast demand. The rejection of predict and provide has posed new challenges for both policy making and modelling. Policy options have become more complex when they do not just have to forecast future total demand and its modal split, but also assess the ways in which policy alternatives may impact on mobility and changes in mobility in turn on the location of economic activity and the underlying generation of both passenger and freight flows.