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 tend 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. 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 and San Francisco and
were afterwards substantially impacted by motorization.