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. Depending on the density and historical conditions, different structural relationships exists 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 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 element of mobility while transit systems have adapted to service specific needs, such as dominant commuting patterns. It represents a context of a low level of density and centrality where development is oriented along highways.
- 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.
At the beginning of the 21st century, public transit is on the rise in many global cities, the outcome of rising congestion, investments in transit infrastructure, and changing social preferences. It is thus likely that transit will play a greater role in the structure and organization of cities. It remains to be seen to what extent and in which context.