Rapid and expanded urbanization occurring around the world involves an increased
number of trips in urban areas. Cities have traditionally responded to growth in mobility
by expanding the transportation supply, by building new highways and/or transit lines.
In the developed world, that has mainly meant building more roads to accommodate
an ever-growing number of vehicles, therefore creating new urban structures. Several
urban spatial structures have accordingly emerged, with the reliance on the automobile
being the most important discriminatory factor. Four major types can be identified at the
metropolitan scale (Figure 7.5):