This book discusses the full economic benefits - and costs - of transport infrastructure and explores ways to make good estimates of the full impact of planned investments on regional and national economies. It argues for proper account to be taken of all relevant economic weaknesses -- those the project is designed to address such as local monopoly pricing, those associated with use of the infrastructure such as environmental externalities, and possible unintended consequences such as impacts on local labour markets. Care must also be taken to verify that net benefits are likely to accrue to those that the project was intended to benefit. Building on recent groundbreaking work in the United Kingdom this publication suggests ways to improve traditional cost-benefit assessments, overcoming reservations that have inhibited the use of CBA in many countries. The main report is completed with examinations of transport project assessment approaches in France, Germany, the United Kingdom and across Europe together with a discussion of an approach to determining optimal levels of investment in transport infrastructure for maximising socio-economic welfare.