Peter Nijkamp and Sytze A. Rienstra
A general phenomenon experienced by almost all cities in the world has been the emergence of green and diffuse suburbs around the city centres. As a result, the population density in cities has decreased significantly. The private car has brought low density living within the reach of large groups of upper and lower middle-class families. In fact, suburbanisation of living is a consequence of various broad changes in society, such as income increase, smaller households, more leisure time, and changing housing preferences. However, suburbanisation is also usually associated with negative socio-economic and environmental impacts, including longer working and shopping trips, increased energy consumption, pollution, accidents, and problematic public transport provision (Masser et al., 1992).
Suburbanisation of living was followed in subsequent years by a second wave of suburbanisation of employment. Thus, dwellings as well as jobs tended to disperse further from urban centres into wider metropolitan areas, a process which may be called extended suburbanisation or counter-urbanisation (Breheny, forthcoming).
The development of decentralised cities, as well as other trends in the economy and society, have caused an enormous increase in car use, even in urban areas. At the same time, the length of commuting trips has increased greatly. Consequently, the external costs of transport have risen drastically; according to recent calculations these may account for some 3% of Gross National Product (Verhoef, 1994).
Development in most large cities of the Western world seems to be following a more diffuse spatial pattern. In spatial planning however, a contrasting concept is gaining much popularity. This concept is embodied in the 'compact city', where housing is provided in a relatively high density form, and where jobs are concentrated in the central city and in a limited number of sub-centres. The compact city has become a leading principle in Dutch physical planning in recent