Assessing the full scale of environmental impacts is essential for effective planning of transport and land use. This is an analysis of transport and land-use planning using strategic environmental assessment (SEA). It establishes the effectiveness of SEA through comparative studies of practice in three countries: Britain, the Netherlands and Germany. The author shows that use of SEA is widespread but far from systematic. He demonstrates the advantages of adopting a systematic application of a comprehensive form of SEA derived from all the major current approaches. Only once this approach is fully understood and systematically applied will all the full benefits be achieved and environmental impacts be minimalized.