The Norwegian Public Roads Administration (NPRA) carries out cost-benefitanalysis for all of its trunk road schemes. This tradition has existed since the early sixties and was formalised in the early seventies. The purpose of cost-benefit analysis is to provide decision makers with informationregarding the economic viability of projects e.g. by how much will traveltime, accidents and air pollution be reduced, and whether these reductions are large enough to offset the investments cost. Essentially, the analyses are performed ex ante. They are thus a prediction of what will occur ifprojects are implemented. A question often raised by the government auditors and the decision makers is whether the predicted benefits and costs are actually achieved. Thus in 2005, the Norwegian Ministry of Transport and Communication authorised the NPRA to carry out ex-post studies of implemented road projects to reveal the extent to which predictions are correct.The purpose of the ex-post re-evaluations is to determine how far the NPRA is achieving its objectives and benefits from its road programme. The NPRA has developed a guideline for conducting ex-post studies focusing on the cost-benefit analysis. The aim is that at least five major road projectsannually should be subjected to ex post studies. This paper reports the findings of ex-post studies in a Norwegian context. Using 8 projects, and recalculating the cost-benefit analysis 5 years after the opening of the project with actual data on traffic, construction costs and accident rates, the accuracy of the forecasted impacts is revealed. Tentative results reveal both underestimation and overestimation of the traffic forecast for theopening year and underestimation of the general traffic growth rate. Investment costs have been both under- and overestimated. Net present value isgreater than forecasted for 7 out of the 8 projects. One of the main reasons for this is that the traffic growth rate has been higher than forecasted. Knowing the history of the project is of importance for the ex post analysis. The divergence between forecasted and actual impacts can be due tothe project being built differently than was assumed in the original analysis. Lack of good documentation for the forecasted impacts for some of the projects have been a challenge for the ex-post evaluation. For the covering abstract see ITRD E145999
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