The transportation-related problems of many of today's cities [?] from a number of interrelated [?]. Growing urban populations and increasing household incomes have [?] to a rise in car ownership, which [?] has created more travel and a demand for more roads. Increasing business and industrial activity has sent more service vehicles onto city streets and has produced more freight traffic. The shape of many cities has also [?] in a demand for more roads, which [?] longer journeys, more congestion, and yet more fuel consumption and pollution.
Income levels [?] the type of transport people use and the number of trips they make. In general, [?] incomes rise, there is a marked increase in vehicle ownership. Increased wealth also [?] more car travel in the form of both new trips, primarily social and leisure, and longer trips.