When consumers and producers decide whether to make a trip, by which mode and at what time, they evaluate the available alternatives on the basis of the costs and benefits of an extra trip for themselves. These are the so-called marginal private costs and benefits. The term “marginal” refers to the change in total costs and benefits due to an extra trip. The marginal private costs include the resource costs (for example, the fuel costs, the vehicle costs and the insurance premium), the taxes, the own time costs and the costs associated with the exposure to the accident risk. However, each trip also causes costs for the other transport users and for society in general. The additional transport users only partly take into account these costs in their decision process, via the taxes and the insurance premia they pay. The costs that are not taken into account are called the marginal external costs. Because of these, the traffic flow resulting from the decisions of the households and firms is larger than what is socially optimal. Moreover, the spread of trips over time is not optimal: too many trips take place in the peak period. The share of the various transport modes and the type of vehicles used is also suboptimal. Policy makers can use various instruments to remedy this situation. Three categories of instruments can be distinguished: economic instruments, command-and-control measures and changes in the infrastructure. Information about the level and structure of the marginal external costs is a crucial input in the design of these policies. The project calculates the marginal external costs of transport use in Belgium. Three main categories of external costs were investigated: environmental costs, accidents and congestion costs. Road damage externalities, which are caused mainly by trucks, are not considered here – with the exception of the air pollution costs related to road maintenance. The environmental costs were analysed by the VITO team, the CES – K.U.Leuven team was responsible for the accident costs and the UFSIA team studied the congestion costs. (Author/publisher)
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