Fast, frequent, reliable public transportation improves city life immensely. But the benefits of high-quality bus or rail service don’t always accrue equally to everyone—especially in cities where high-quality transit lines are few and far between.

Fortunately, the Center for Neighborhood Technology’s AllTransit tool has the power to analyze who exactly benefits from good transit at a level of detail that was never before possible.

The core of AllTransit is its ability to assign a transit Performance Score to almost any address in the country. Just as useful, however, AllTransit can distinguish between the transit lines that create communities of regular riders and the infrequent bus and rail service that passes for transit in too many places.

Most people who live in cities live near transit…

For our analysis, TransitCenter examined the 25 largest cities in the U.S. plus three more (Atlanta, Cleveland, and Miami) that are smaller but have heavy-rail transit systems.

The U.S. is often thought of as having a select few “transit cities”—roughly, those in the northeast, on the west coast, and Chicago. But AllTransit shows that more urban Americans live near transit than than this stereotype might suggest. In every one of the cities analyzed, a majority of the population lives within walking distance of a bus or rail stop—even Jacksonville, Florida, which at 875 square miles is larger than 27 sovereign countries. In 13 of the 28 cities, more than 90 percent of people live within walking distance of transit.

…but usually that transit isn’t very useful.

Despite these encouraging statistics, most of the transit described above is of poor quality—that is to say, it isn’t frequent enough to be a reliable option transportation option.

AllTransit sets a fairly strict definition of “high-quality” transit. A train or bus line must run at least 672 times per week, or every 15 minutes on average, to qualify. Using this cutoff, here is how the provision of frequent transit exists across the 28 cities:

AllTransit/The Center for Neighborhood Technology

A few key facts emerge from this chart. First, at the cutoff used by AllTransit the number of large U.S. cities with no high-quality public transportation is substantial. San Antonio, which is the busiest bus-only transit system in the country, has no lines that qualify as high-frequency. Neither does Phoenix, which has recently opened new light rail and rapid bus lines. Even Atlanta, with its relatively large subway system, doesn’t run enough late-night and weekend service to make the cut. In all, 13 of the 28 cities (comprising 12.2 million people) fall into this category of offering no high-quality transit whatsoever.

Second, there’s no clear-cut relationship between the amount of overall transit access in a given city and the amount of high-quality transit access. Both Detroit and Cleveland offer near-universal transit coverage, but each has only one high-frequency line. In Cleveland, it is the well-regarded HeathLine BRT, but in Detroit it is the downtown People Mover, an elevated loop line built in the 1980s that has been called “The World’s Most Pointless Transit System.”

Access to good transit is often inequitable

AllTransit also incorporates demographic data from the census, allowing comparison of the communities with access to high-quality transit and those with access to any kind of transit.

AllTransit/The Center for Neighborhood Technology

The chart above shows this discrepancy in the 15 cities from the list above that offer high-quality transit service. The darker bars on top show the racial composition of residents who live within half a mile of a high-frequency transit stop. The lighter bars below show the same for those within half a mile of any transit stop.

Notably, in cities with fewer high-frequency transit lines there tends to be a greater demographic skew among people who live near quality transit. Often, but not always, those neighborhoods have substantially smaller proportions of people of color.

Two of the most notable examples of this type of city are Denver and Houston, which are both investing in new transit lines and—in Houston’s case—redesigning bus routes to better serve riders.

In Houston, only a few routes meet AllTransit’s standard of high frequency: the city’s three light rail lines and the 82-Westheimer bus. (METRO Houston board member Christof Spieler has disputed AllTransit’s methodology.) Black and Latino Houstonians comprise 69 percent of those living within walking distance of transit, but 54 percent of those close to these high-frequency lines. For white people, the figures are 24 percent and 36 percent respectively.

To better illustrate the discrepancy, compare AllTransit’s frequent service map of Houston to a map from the New York Times’s recent “Mapping Segregation” project. Though some heavily black and Latino neighborhoods north of downtown and south of Westheimer Road are close to the high-quality routes, vast majority-minority areas on the southeastern side of the city have no access to comparably frequent bus or rail lines.

AllTransit/The Center for Neighborhood Technology

The New York Times

The situation is somewhat different in Denver. Though an ambitious regional rail system is under construction, the area of current high-quality transit is small and shaped like a hockey stick, running along East Colfax Avenue (with its frequent #15 bus) before jutting northwest into downtown. These neighborhoods are overwhelmingly white—70 percent, according to AllTransit, and just 15 percent Latino. The numbers are a stark contrast to the community of transit-accessible Denver residents overall, which is 53 percent white and 31 percent Latino. Most Latinos in Denver live on the western end of the city, on the opposite side of Interstate 25 from downtown.

AllTransit/The Center for Neighborhood Technology

The New York Times

The tendency for high-quality transit to serve whiter neighborhoods is not universal. In Cleveland, for instance, the HealthLine runs through some census tracts that are almost entirely African American.

But the more important takeaway might also be the most obvious: cities with many high-quality transit lines are much better at providing equitable high-quality transit service. Places like New York, Chicago, and San Francisco didn’t set out with the explicit intention of building transit systems that would reach as diverse a group of residents as possible. By having frequent transit networks that span large swaths of the city, however, they are able to provide service to many different communities relatively equally.