Mobility is a key dynamic of urbanization, and the associated infrastructure invariably shapes the urban form – the spatial imprint defined by roads, transport systems, spaces, and buildings – of cities. By 2005, approximately 7.5 billion trips were made in cities worldwide each day. In 2050, there may be three to four times as many passenger-kilometers travelled as in the year 2000 (infrastructure and energy prices permitting). Freight movement could also rise more than threefold during the same period.
Yet, despite the increasing level of urban mobility worldwide, access to places, activities and services has become increasingly difficult. Owing to urban sprawl – the horizontal, low-density growth of cities over vast areas – distances between functional destinations such as workplaces, schools, hospitals, administration offices, or shopping amenities have become longer, leading to a growing dependency on private motorized transport and other car-centered mobility. Consequently, widespread congestion and traffic gridlock have now become the norm in many cities, impacting urban life through negative externalities such as pollution, noise stress, and accidents.
In some cities, the physical separation of residential areas from places of employment, markets, schools, and health services force many urban residents to spend increasing amounts of time, and as much as a third of their income, on transportation. In the developing world, and especially in African cities where walking can account up to 70 per cent of all trips, this low-density horizontal urban development causes further exclusion of the urban poor. Due to transport poverty, many residents cannot afford to travel to the city centres or to areas where businesses and institutions are located, depriving them of the full benefits offered by urbanization.
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