Building safe ways for children to bike and walk to school is more than just a way of encouraging kids to go outside and get active. According to a new study, it’s also an investment that reaps millions of dollars in societal gains. In other words, smart walking and biking infrastructures for kids make good economic sense.

Published in the July issue of the American Journal of Public Health, the study examined the cost-effectiveness of Safe Routes to School (SRTS) infrastructure in just one city — New York City. SRTS was initially enacted in 2005 as part of a massive federal transportation bill known as the Safe, Accountable, Flexible and Efficient Transportation Equity Act and was supported with more than $600 million that states could use to build new sidewalks and bike lanes and enhance road safety features. In New York City alone, the study found that SRTS is linked with an overall net societal benefit of $230 million as well as 2,055 quality-adjusted life years gained, which measures the quality and quantity of life gained through a health intervention. And like many such public health ROI (that’s return on investment) studies, that’s a conservative estimate.

“To be honest, I wasn’t really sure what we would find,” said study co-author Peter Muennig, an associate professor of health policy and management at Columbia University Mailman School of Public Health. “Changes to intersections are not that expensive and they last a really long time, but on the other hand, the chance of any one person getting killed at an intersection is fairly tiny. So we went into it not really knowing what would happen. But when you look across the whole city, the effect was pretty big.”

To conduct the study, which examined the impact of SRTS on everyone and not just schoolchildren, Muennig and his study colleagues focused on intersections with histories of high injury rates and estimated the long-term impact of SRTS improvements on injury and its associated economic and quality-of-life costs. They found that SRTS saves $5,500 per user and results in a net gain of about 0.02 quality-adjusted life years per user, noting that “in the parlance of cost-effectiveness analysis, SRTS is said to ‘dominate’ a no investment strategy, indicating that every dollar spent on SRTS saves both money and lives.” When all users of SRTS improvements are taken into account over 50 years, it comes to a net benefit of $230 million and more than 2,000 quality-adjusted life years gained. The study also found that even if the gains are isolated to just school-age children, SRTS still saves money over the long run.

Muennig told me that this is a conservative estimate, as it doesn’t account for other ways SRTS may impact health, such as the impact that increased physical activity can have chronic diseases such as obesity. Noting that SRTS has been found to increase walking and biking among children (click here for a wealth of evidence on inclusive transportation planning, physical activity and child health from the Safe Routes To School National Partnership), Muennig and co-authors Michael Epstein, Guohua Li, and Charles DiMaggio write:

About one third of obese children become obese adults, and obese adults accrue many additional costs, such as lost productivity costs, and obesity accounts for upwards of 10% of all medical costs. Moreover, the rise in obesity expenditures outstrips the medical portion of the consumer price index in part because obesity rates are increasing and in part because, as the population ages, the obese incur disproportionate costs.Were SRTS to prevent a small number of cases of obesity in each cohort, this benefit alone would likely pay for the entire program over time.

Muennig said the SRTS benefits that he and his colleagues found would likely be even greater in communities that don’t already have the extensive pedestrian networks that New York City does. In the context of a serious obesity epidemic in the United States, he added that smarter transportation and urban planning that supports safe walking and biking could be a key component to creating healthier populations.

“(Efforts such as SRTS) get people out and moving around in ways that don’t require a lot of volition on their part,” he told me. “Urban redesign to reduce dependence on motor vehicles has great promise. From a theoretical standpoint, it holds much greater promise than hoping people will diet and exercise on their own.”

Muennig said he hopes advocates will use his findings to justify continued investments in pedestrian and bicycling infrastructure and enhancement, though he knows it can be a tough sell. In the latest iteration of the federal transportation funding bill, now known as Moving Ahead for Progress in the 21^st Century Act, or MAP-21, SRTS was combined with other biking and walking programs and funding was cut by more than 30 percent.

“It’s a tough funding environment in general,” Muennig said. “There’s a strong movement toward across-the-board budget cuts and we’re not thinking carefully enough about which cuts are targeting investments that will produce monetary returns and which are needed to address the deficit. …If you don’t have functioning roads, you don’t have a functioning economy. If you have a sick and obese population, you can’t have a functioning economy. We need to think carefully, on both the left and the right, about which kinds of investments will produce returns over the long run.”

To request a full copy of the latest SRTS study, visit the American Journal of Public Health. To learn more about Safe Routes to School, visit Safe Routes to School National Partnership. And to read more about why transportation design matters to community health and how inadequate public transportation disproportionately affects low-income workers, read Liz Borkowski’s recent post here.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for more than a decade.