We considered the following five metrics in particular:

The first two metrics reflect the efficiency of each city’s transit system. Shorter commute times for transit users reflect a more efficient system. Likewise, if driving is significantly faster than transit, the system is not offering an attractive alternative on practical or economic grounds.

The third and fourth metrics reflect the availability of transit. More people using public transit indicates a system with greater coverage and more capacity. The fifth metric reflects the overall quality of the system. In many systems, transit serves as a citywide backup plan. It is used primarily by people who cannot afford to own a car or to drive. A smaller income gap reflects a system that provides an attractive option for all commuters.