Source: Adapted from R. Cervero (1998) The Transit Metropolis, Washington, D.C.: Island Press.
Urban transit systems played an important role in shaping urban form in the late 19th up to the mid-20th century. Then, the massive diffusion of the automobile and highway systems broke this relationship, which resulted in a growing divergence in urban forms, land uses, and mobility. Depending on the density and historical conditions, different structural relationships exist between transit and the urban form:
- Adaptive cities. Urban transit is the dominant element of mobility, and the urban landscape has been adapted to service the general needs of transit-oriented urban mobility. They have a high level of density and centrality where development is oriented along transit lines and stations.
- Adaptive transit. The car is the dominant mobility element, while transit systems have adapted to service specific needs, such as dominant commuting patterns. It represents a context of low density and centrality where development is oriented along highways, with the city shaped as a grid.
- Hybrids. Represent a level of tradeoff between the mobility requirements of transit and the automobile. The CBD and subcenters are serviced by major transit lines where subsidiary lines are converging. It represents lower-density cities with a weaker CBD and subcenters in peripheral areas.
At the beginning of the 21st century, public transit is on the rise in many global cities, resulting in congestion, investments in transit infrastructure, and changing social preferences. Thus, transit will likely play a greater role in the structure and organization of cities. It remains to be seen to what extent and in which context.