At the same time, however, transport networks need to be developed in ways which minimize unacceptable adverse impacts. To date the rapid urbanization of Asian cities has, for the most part, resulted in cities that are heavily congested, are poor in urban amenity, suffer high levels of air pollution, emit substantial amounts of C02, inefficiently use scarce land resources, and present unequal access to opportunities for their residents. In the case of road congestion, the degraded amenity particularly affects and decreases the use of other, lower polluting road users, namely public transport, cycling and walking.