This research project had the aim to develop a set of harmonised guidelines for assessing transport projects and their associated costs at the European level. It reviewed and analysed existing project assessment practices in Member States, especially issues as time and congestion; accident risk reduction; health impact of pollution; and infrastructure costs. The guidelines developed a stringent methodology for the estimation of costs and benefits of planned transport projects reflecting the state of the art. The research contains four case studies in Europe, where the proposed guidelines were tested.