Quantification of marginal social costs of road transport: what are the main components?

The current concern with sustainability rightly requires those involved with transport to consider carefully the sustainability of the transport sector, and in particular its contribution to greenhouse gas emissions. However, it is important to remember that greenhouse gases are just one of the costs of transport systems, and it makes no sense therefore to take decisions about transport systems based on the impact on greenhouse gas emissions alone. Against this background, the paper discusses the state of research in estimating marginal external costs of road transport and presents the results of two case studies. These suggest that under peak traffi c conditions congestion costs are by far the most important externalities of road use. Accidents, wear and tear and noise costs all appear to be more important than global warming. These results stress that reducing global warming costs, important though they are, should not be the sole priority of transport decisions. Our results suggest that other costs are also very important and need to be taken into account in pricing and investment decisions.