Transportation and the Urban Spatial Structure

Transportation and the Urban Spatial Structure

Although there are an extensive variety of urban spatial structures, a large share of metropolitan areas can fit into four types:

  • Type I (Completely motorized). This spatial structure is characterized by low to average land use densities. The automobile-oriented network assumes free movements between all locations. Public transit has a residual function, while a significant share of the city is occupied by infrastructures servicing the automobile, notably highways, on-street parking, and parking lots surrounding activity centers. Thus, most activities are designed to be accessed by the automobile, which requires a massive network of high capacity highways, underlining that urban efficiency and productivity are dependent on road accessibility. Secondary roads converge at highways, along which small centers are located, notably nearby interchanges. This system reflects North American cities where urban growth occurred in the second half of the twentieth century, such as Los Angeles, Phoenix, Denver, and Dallas.
  • Type II (Weak center). Average land use densities and a concentric pattern are the main characteristics of such urban areas. The central business district is relatively accessible by the automobile and is the point of convergence of the transit system, which tends to be under-used and requiring subsidies. Most urban areas cannot be cost-effectively serviced with a transit system, so services are often oriented along major corridors. More recently, ring roads favored the emergence of a set of small centers at the periphery, notably at the convergence of radial lines. Some of them are effectively competing with the central business district for the location of economic activities. This system is often related to older cities that emerged in the first half of the twentieth century and were substantially impacted by motorization, such as Melbourne and San Francisco.
  • Type III (Strong center). This spatial structure characterizes cities with high land use density and high accessibility levels to urban transit. There are thus relatively fewer highways and parking spaces in central areas, where a set of high capacity public transit lines are servicing most of the mobility needs. Thus, the productivity of this urban area is mainly related to the efficiency and accessibility of its public transport system. The convergence of radial roads and ring roads favors the emergence of secondary centers, where locate activities that could no longer be able to afford the high costs related to the central district. This system characterizes cities having important commercial and financial functions and having grown in the 19th century, such as Paris, New York, Toronto, Tokyo, Sydney, and Hamburg. It also characterizes cities that recently undertook a fast wave of urbanization, such as in China; the traditional high-density core is complemented by the setting of sub-centers in a lower density setting.
  • Type IV (Traffic limitation). Represents urban areas that have implemented traffic control and modal preference strategies in their spatial structure. Commonly, the central area is dominated by public transit. Limitations in automobile usage in central areas are enforced for a variety of reasons, such as preserving its historical character or avoiding congestion. Through a “funnel” effect, the capacity of the road transport system is reduced, the closer one gets to the central area. Public transit is used in central areas, while individual transportation takes greater importance in the periphery. Between suburbs and the central city are interfaces connecting individual (automobile) and collective forms of transportation or between low capacity collective transportation (bus) and high capacity collective transportation (metro, rail). Several cities are implementing this strategy, namely through congestion pricing, as it keeps cars from the central areas while supporting the bulk of the mobility in the suburbs. This system typifies cities having a long planning history favoring public transit. London, Singapore, Hong Kong, Vienna, and Stockholm are good examples of this urban transport structure.