If you build a new suburb, you hook it up to the rest of the world with roads. But if you want that same suburb to join an existing public transport network, that takes a lot more planning. That leaves a lot of people without access to public transport, and those are often the people who need it most—people who can't afford cars, for example.
In order to see how well communities are doing in this regard, a new metric has been developed to measure how many people live within short walking distance (1 km, or 0.6 miles) of public transit. It's called People Near Rapid Transit (PNT), and has so far been applied to 26 cities around the world. The short form: Paris gets a perfect score, with 100% of the population within a kilometer of a transit station, and the L.A. metropolitan area gets a ridiculously low 11% score. Barcelona scores 99%, while the Washington metro area scores 12%. If you only count the downtown districts of Washington and L.A., then they score 57% and 24%, respectively, but that is to miss the point: These cities are poorly served by public transport largely because of their urban sprawl, which encourages car use.
"Very few cities are investing in the rapid transit systems that serve the less wealthy communities living outside of the urban core, even in Europe and especially in North America," writes the Institute for Transportation and Development Policy (IDTP), the organization that came up with the PNT.
The PNT metric is designed to be both a measure of the practical, everyday mobility possible in a given city, and also to allow very different cities to be easily compared (and possibly shamed). It is also easy to measure, as all the information needed is publicly available on transit maps. Other accessibility metrics can be hard to gather data on. Access to employment, for example, can be a good measure of both the transit system, and of the economic health of a city, but "the main difficulty with this approach is acquiring location-based employment data," says the report. "While accurate data is often available in high-income countries, it is much more difficult to find in low- and middle-income countries."
Public transit is the fastest way to get people around a city, and the most efficient. It also reduces pollution, and deaths due to crashes. It also enables low-income residents to commute to their jobs without requiring that they own an expensive-to-run car. In this context, PNT isn't just a metric that allows us to rank cities, but a goal for cities to work toward. If all the residents of a city are within a short walk of transit, then many problems start to go away. Cities can be much more ruthless when curbing car use, for example, if 100% of the population has easy access to alternatives. It's anecdotal, but perhaps Paris's 100% PNT score has something to do with its mayor Anne Hidalgo's willingness to ban cars from its center, and to pedestrianize major roads.
The PNT isn't perfect. It measures the direct distance to the nearest public transit stops, so you may end up having to walk farther if there are "urban barriers" or other difficult topography in the way. But its utility, its comprehensibility, and the relative ease with which it can be deployed make it a rather compelling metric nonetheless. Imagine if the PNT became a point of pride for a city, a score to be shown off to both tourists and future residents. Then we might start to see some changes.