An international review of evidence and new theoretical development reported by the UK Standing Advisory Committee on Trunk Road Assessment (SACTRA) is discussed. The assumption of perfect competition is debated and it is considered a reasonable basis underlying cost benefit analysis. However it is important that the projected time savings implicit in the project are achieved, that the environmental impact study has been properly conducted and taken into account, and that the time savings initially resulting from the scheme will be lost as the economic benefits of the scheme are fully realised. In the case of imperfect competition, it is possible that the wider economic impacts are not just a change in the form of initial user impacts, but may be additional to them. This additional impact may be positive or negative, depending on the relative strengths of the economies which are linked by the development. Practical processes for the appraisal of the economic impacts of transport project proposals are outlined.
Abstract