The induced travel: overview and perspectives

The animated debate on induced traffic is going on since long time, as the first studies on this matter go back to the first half of the XXth century. This report intends to give an overview of this argument, analysing the historical evolution of the approaches used in the studies on the induced travel and of the models carried out to take into account this phenomenon. The starting point will be the definition of the concept, necessary because either the lack of understanding or the misunderstanding between the different point of views can partly be generated by different meanings given to the concept; the other part of disagreement can lay on different interests involved in road construction. Then, the overview of the studies carried out in Europe and USA will allow for the understanding of the mechanism of causality between the supply and demand and will try to answer to the questions: “does the transport user’s behaviour generate the policy makers’ decisions” or “does the policy makers’ decisions generate the transport users’ behaviour” ?. Lastly, some considerations about the acceptance of the analysed concept and the answer of Administrations and relative eventual interventions are given. It emerges quite clear from this work that the behavioural responses are the real focus and that an adequate policy on the land use that drives the transport systems is the unique way to have a real sustainable development either of land use or of infrastructures. To manage the transport demand through land use could control the transport demand, deviating it towards sustainable solutions. In addition, neglecting the induced travel effects leads to underestimate the impacts due to transport systems. That generally leads to a non-sustainable policy, deteriorating rather than improving the quality of life in urban and extra-urban areas.