Third, public transportation can improve the quality of life in our cities. It provides an
alternative means of accessing a wide range of employment and social activities for many
people who cannot or choose not to drive. Public transportation also allows for and is made
viable by denser land use patterns that often entail quality of life benefits such as more
shopping and housing options within a neighborhood (Newman and Kenworthy 1996). Given
the general benefits of public transportation and the positive feedback effect of providing high
quality service, we might ask what makes a good public transportation network.
One challenge in definitively characterizing a good public transportation network is
that the appropriate design depends largely on passenger demand, which in turn depends on
factors such as service quality', land use density, and demographics. Moreover, the network
layout is most often constrained by the existing spatial structure of the region it serves.
Certainly, we observe some cities with a grid network structure, for example Toronto and
Mexico City, and others with a predominant radial structure, for example Chicago's rail and
Munich's S-Bahn regional rail system. Regardless of overall structure, a primary objective in
public transportation planning should be to provide direct service between trip origins and
destinations for which there is sufficient demand, for example from high-density suburbs to
the central business district