Taking Policy Uncertainty into Account in Traffic Forecasts ? the Fréjus Tunnel Example

Taking Policy Uncertainty into Account in Traffic Forecasts ? the Fréjus Tunnel Example


M Kouwenhoven, Significance, NL; E Kroes, Significance / VU University Amsterdam, NL; G de Jong, Significance, NL / ITS, University of Leeds, UK / NEA, NL


A tool was developed to take uncertainties in macro-economic inputs and in policies of other parties into account when producing traffic forecasts for the Frejus tunnel between Italy and France.


Taking policy uncertainty into account in traffic forecasts ? The Fréjus tunnel example

Marco Kouwenhoven, Significance
Eric Kroes, Significance / VU University Amsterdam
Gerard de Jong, Significance / ITS Leeds / NEA

Traffic forecasts are widely used for cost-benefit analyses of proposed infrastructure investment projects. In recent years it has been accepted that forecasts are by definition uncertain, and that it is desirable to take this uncertainty into account in the analyses. The uncertainty is not only due to the fact that a model is a simplification of a complex reality, but also to uncertainty in the inputs of the model, such as the expected economic growth. Previous studies have shown that traffic models themselves are often not bad at all, but that the main cause of deviations between traffic forecasts and observed traffic volumes are the errors in these model inputs that really drive the growth of travel (e.g. Gunn and van der Hoorn, 1998, De Jong et al., 2007).

Macro-economic data are not the only inputs for travel models. Another important group of factors that influence traffic forecasts, but are external to the decision-maker for a specific project, are the policies of other authorities and organisations (both policies that have already been decided upon, but have not yet been implemented, and new future policy decisions). Uncertainty in these policies (when will a certain tax be introduced? What will be the level of a certain charge? When will a certain safety measure become compulsory?) can also be an important factor. However, these uncertainties are usually not taken into account in traffic forecasting studies.

The Fréjus tunnel is an important toll road connection between France and Italy and is part of the trans-European transport network (TEN-T). The operators of the tunnel use traffic forecasts to estimate their future revenues, which in turn are being used to negotiate subsidies from the road authorities in Italy and France. In the forecasts several types of uncertainties are explicitly taken into account: uncertainties in the key drivers of traffic growth, such as GDP, but also uncertainties caused by policies of other parties affecting traffic volumes: when will the Lyon-Torino high-speed rail service open (for passengers, and for freight)? What will be the cost for the users of that service? What European environmental policies will be introduced that might affect the maximum flows of trucks through the Fréjus tunnel in the long run, etc.

We have developed a tool to take all these uncertainties into account and present the outcomes in a clear and intuitive way that is useful for stakeholders. Similar tools have also been developed for other projects in The Netherlands and France. In the paper we will demonstrate an example of this tool and we will discuss the importance of taking uncertainties into account for policy making.


Gunn, H.F. and A.I.J.M. van der Hoorn (1998) The Predictive Power of Operational Demand Models, paper presented at the PTRC/AET European Transport Conference, Loughborough University.

Jong, G.C. de, A.J. Daly, M. Pieters, S, Miller, R. Plasmeijer and F. Hofman (2007) Uncertainty in traffic forecasts: literature review and new results for The Netherlands, Transportation, 34, pp. 375-395.


Association for European Transport