Urban Transport XXI contains the proceedings of the 21st International Conference on Urban Transport and the Environment. The series of annual conferences organised by the Wessex Institute was first held in 1995. Transportation in urban areas, with its related environmental and social impacts, is a topic of significant concern for policymakers in both municipal and central government and for the urban citizens who need effective and efficient transport systems. Urban transport systems require considerable studies to devise and then safeguard their operational use, maintenance and safety. Transportation systems produce significant environmental impacts and can enhance or degrade the quality of life in urban centres. Clearly the challenge of providing effective and efficient transport systems in urban settings remains an acute concern, with financial, political and environmental constraints limiting the ability of transport system planners and operators to deliver the high quality outcomes expected by the public.