Flickr/Neon Tommy

It all depends on how active they were to begin with, new research finds.

The widely held notion that better public transit encourages more physical activity feels true. It fits the dualistic picture of urban/suburban health that city boosters often paint: Drivers roll from garage to parking lot with nary a step taken, while bus and rail riders get their hearts pumping on brisk walks or bike trips to and from the station. City officials love to tout transit’s health benefits in marketing campaigns, as do planners, developers, and transit advocates.

But the connection doesn’t seem to be so black-and-white. New findings by the University of Southern California and UC Irvine published in Transportation Research should give “walkability” proselytizers some pause. This is one of the most comprehensive studies to date examining how access to light rail influences physical activity, and it found that having rapid transit nearby can boost steps for some—but can decrease them for others.

The study centered on neighborhoods between downtown Los Angeles and Culver City along the Expo light rail line, which opened in spring 2012. (The line’s extension to Santa Monica opened earlier this summer, and was not part of the study.) Besides bringing rail to these parts of south L.A. for the first time in six decades, the Expo Line also accompanied by fresh landscaping, dedicated bike lanes, and sidewalk improvements along its alignment. The researchers sent study invitations to thousands of households in this area. About 200 people agreed to participate in a weeklong survey tracking their daily walks, about six months before the line opened. Of those, 73 also wore an accelerometer device on their hips for seven days, taking it off only for sleep and periods of dedicated, intense exercise (such as a pickup basketball game).

Before and after shots of neighborhoods near two new Expo Line stations show dramatic changes in the streetscape. (Transportation Research)

Among these individuals, the researchers separated out a treatment group—defined as folks living within a half mile of a new Expo station—and a control group that lived further away. The demographics of both groups were extremely similar: About two-thirds were female, the average age was 52, about half were African American, and most fell into the middle of the income spectrum. The subjects repeated both the self-reported and accelerometer surveys six months after the Expo Line opened.

The results: Folks who lived within a half a mile of the Expo Line certainly increased their use of transit after it opened. But there didn’t seem to be a significant jump in how physically active they were—at least not without controlling for how physically active the subjects were to begin with. Indeed, when the researchers did control for baseline activity, with all other demographic characteristics being equal, individuals who were already pretty active turned out to be somewhat negatively affected by light rail access. That is, their daily physical activity, as measured by the accelerometers, fell ever so slightly, probably as a result of substituting rail for walking or bike trips.

This map shows the study area along the Expo Line. Starred addresses inside circles represent individuals within a half-mile of a station, while starred addresses outside circles were further away. (Transportation Research)

On the other hand, folks who didn’t move around much to start with showed modest increases in their daily levels of walking and physical activity after the Expo Line opened. That’s an important finding, says Andy Hong, the lead author and a recent Ph.D. graduate from USC’s Department of Urban Planning and Spatial Analysis. “At least, light rail transit is a good prescription to a sedentary population that typically maintains less healthy lifestyle,” he says via email. Officials and advocates serious about spreading transit’s health benefits might consider targeting outreach campaigns more carefully at people who aren’t moving much to begin with. By the same token, they should be careful not to overstate what those benefits are, or to whom they extend.

Only a couple of other studies to date have taken this experimental approach to analyzing the link between healthy travel choices and transit access, and what they found was pretty consistent with this new research. If this seems to contradict what you’ve read in the past, it’s true that a wealth of studies have found strong correlations between physical activity and transit use. But most of this research has been “cross-sectional” in nature, revealing correlations taken from a mere snapshot in time. Though it has its own flawsthe sample size and geographic range weren’t very big, for example—this USC/UCI analysis was longer term than those studies, and it looked at before-and-after effects of a new train.

Of course, even if some otherwise-active people end up sitting more as a result of a new train or rapid bus route, that doesn’t negate the all the other good things that quality transit can bring: a wider job market, a chance to save on gas money, and cleaner air, to name a few. Still, the research is a sobering reminder that there’s a lot we don’t know about public health and urban planning. Transit is often described as the linchpin in a neighborhood’s walkability, but that might depend on whose shoes you’re in.

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