(Source)
Type I - Completely Motorized Network
Characterized by low to average land use densities, this automobile-oriented city assumes free movements between all locations. Public transit has a residual function while a significant share of the city is occupied by structures servicing the automobile, notably highways and large parking lots. Most activities are designed to be accessed with an automobile. This type of urban structure requires a massive network of high capacity highways to the point that urban efficiency is based on individual transportation. Secondary road converges at highways, along which small centers are located, notably nearby interchanges. This system characterizes recent cities in a North American context where urban growth occurred in the second half of the twentieth century, such as Los Angeles, Phoenix, Denver and Dallas.
Type II - Weak Center
These cities are characterized by average land use densities and a concentric pattern. The central business district is relatively accessible by the automobile and is the point of convergence of the transit system, which tend to be under-used and requiring subsidies. The urban area cannot be cost effectively serviced with the transit system, so services are often oriented along major corridors. In many cases, ring roads favored the emergence a set of small centers at the periphery, notably at the convergence of radial lines, some of them effectively competing with the central business district for the location of economic activities. This system is often related to older cities, which emerged in the first half of the twentieth century, such as Melbourne, San Francisco, Boston, Chicago and Montreal, and were afterwards substantially impacted by motorization.
Type III - Strong Center
Characterizes cities having a high land use density and high levels of accessibility to urban transit. There are thus limited needs for highways and parking space in the central area, where a set of high capacity public transit lines are servicing most of the mobility needs. The productivity of this urban area is thus mainly related to the efficiency of the public transport system. The convergence of radial roads and ring roads favors the location of secondary centers, where activities that could no longer able to afford a central location converge. This system characterizes cities having important commercial and financial functions and having grown in the 19th century, such as Paris, New York, Shanghai, Toronto, Sydney and Hamburg.
Type IV - Traffic Limitation
Represents urban areas that have efficiently implemented traffic control and modal preference in their spatial structure. Commonly, the central area is dominated by public transit. They have a high land use density and were planned to limit the usage of the automobile in central areas for a variety of reasons, such as to preserve its historical character or to avoid 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 a greater importance in the periphery. Between suburbs and the central city are places of interface between individual (automobile) and collective 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, particularly in socialist economies. London, Singapore, Hong Kong, Vienna and Stockholm are good examples of this urban transport structure.
Classes of Cities according to Urban Form in relation to Transit
(Source)
- 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. 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. It is a context of 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.
(Interesting discussion following the above categorization)
Contemporary land development tends to precede the introduction of urban transit services, as opposed to concomitant developments in earlier phases of urban growth. Thus, new services are established once a demand is deemed to be sufficient, often the subject of public pressures. Transit authorities operate under a service warrant and are often running a recurring deficit as services are becoming more expensive to provide. This has led to a set of considerations aimed at a higher integration of transit in the urban planning process, especially in North America, where such a tradition is not well established. Still, in spite of decades of investment, North American public transit ridership has roughly remained the same.
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