Do road planners produce more 'honest numbers' than rail planners?: An analysis of accuracy in road-traffic forecasts in cities versus peripheral regions

Based on a review of available data from a database on large-scale transport infrastructure projects, this paper investigates the hypothesis that traffic forecasts for road links in Europe are geographically biased with underestimated traffic volumes in metropolitan areas and overestimated traffic volumes in remote regions. The present data do not support this hypothesis. Since previous studies have shown a strong tendency to overestimated forecasts of the number of passengers on new rail projects, it could be speculated that road planners are more skilful and/or honest than rail planners. However, during the period when the investigated projects were planned (up to the late 1980s), there were hardly any strong incentives for road planners to make biased forecasts in order to place their projects in a more flattering light. Future research might uncover whether the change from the 'predict and provide' paradigm to 'predict and prevent' occurring in some European countries in the 1990s has influenced the accuracy of road traffic forecasts in metropolitan areas.