The Ministry of Transport, Water Management and Public Works asked CE to undertake an explanatory analysis of five authoritative European studies on the unpaid costs of road and rail transport. The motive for the study was the fact that policy-makers in the field of transport pricing policy often cannot see the wood for the trees, as each new study at first sight appears to yield entirely different results. This apparent 'disagreement among economists obviously makes it hard to back up pricing policy. The analysis shows that the economic uncertainties are not as great as they might seem. While there are certainly differences among the studies, these are due not so much to differences in economic valuation as differences in the indices used in particular, for emissions and accident risks and differences in a limited number of normative assumptions. For example, are the full costs of infrastructure maintenance to be passed on to users? Should the government protect its citizens against risks they themselves induce (through compulsory seat belts, for example)? How serious should climate policy be taken? Once these kind of choices have been made, the differences in cost estimates prove to be fairly minor.