Study: Fewer Cars on the Street = Healthier Kids

Kids_Crossing_Street.jpgFewer cars means more walking and healthier kids. Image: jeweledlion via Flickr.

Could reducing traffic near children’s homes help America combat its obesity epidemic? A new study conducted by UC Berkeley professor Michael Jerrett strongly suggests the answer is yes.

Obesity rates are steadily increasing — more than one-fifth of New Yorkers are now obese, and even that figure is well below the national average. With obesity strongly linked to dangerous diseases like diabetes and asthma, a great deal of research has
gone into uncovering the factors at work.

The quality of the built environment matters tremendously. Everything from mixed-use development to street connectivity to park access has been shown to affect physical activity, Jerrett notes, thus affecting obesity rates.

The new research, published in the journal Preventive Medicine, makes a crucial addition to what we know already. Jerrett shows that not only does the built environment matter, but traffic volumes matter too. His team’s long-term study tracked children from across Southern California, starting from ages 9-10 and continuing through high school. Controlling for a wide variety of factors, they compared the children’s body mass indexes (BMI) to the density of traffic near their homes.

Children living within 150 meters of high-traffic areas were found to have, on average, BMIs five percent higher than those living near low-traffic areas. Only the immediate surroundings seem to matter: Traffic levels within 300 or 500 meters didn’t affect BMI.

The researchers put forward two explanations for why high traffic contributes to obesity. The first is that real or perceived danger from cars reduces walking and biking. The other is that too much traffic contributes to high asthma rates, which make physical activity more difficult and less frequent.

James Sallis, director of the Active Living Research Program at the Robert Wood Johnson Foundation, which commissioned the study, says Jerrett’s research stands out because it tracked a large sample of kids for a long period of time, giving it strong scientific value. “This actually points to some solutions,” he added, noting that not every study commissioned by the program has such clear implications for policy.

Just last week, New York City released its Active Design Guidelines, bringing together the city’s transportation and city planning departments with the health department. Jerrett’s report suggests that policies that help reduce traffic — like congestion pricing, performance parking, and off-street parking reform — should be a necessary component of the effort to fight obesity and improve New Yorkers’ health.

  • So does this mean it’s healthier to live in rural areas, where traffic is thinner?

  • Evan- good question about rural areas.

    It is not necessarily healthier to live in rural places. The Rural Assistance Center website had good info about the reasons why:

    It’s not easy to walk or bike in rural communities because land use is designed primarily for driving. Destinations are spread out and connected by busy state highways and thoroughfares without bike lanes or safe street crossings. Traffic may be thinner on back country roads, but in order to get to places like shopping or services, one has to get in the car and drive.

  • for info speficially on the challenges of walking/biking to school in rural areas, see:

  • Ian Turner

    Evan, note that the study “Controlled for a wide variety of factors”, which presumably included population density.

  • Makes total sense!

    I’ve always argued that volume is the critical factor to determin if a road is bicycle friendly too. A road could be narrow and have a 50mph speed limit but if only one car is passing you every ten minutes, then the other two limiting factors to bicycling safety (speed limit and width) are mostly mute and the road is relatively safe to ride.

    Another good reason to site elementary schools (in particular), deep within neighborhoods and off the major roads.

  • Too bad the study didn’t include pulmonary funcion tests, so that the alternate factor associated with risk of higher BMI–decrement in pulmonary function due to nearby traffic during pulmonary development in children–coud have been confirmed or disproved. Fear of traffic and pulmonary function deficit are two very different mechanisms for producing obesity; the possbility that either might be entirely responsible for the observed effect makes it hard to knwo what to do, except for simply getting rid of traffic (not a bad idea, of course). It would be great to see a follow up study with PFTs here in NYC.

  • @ Debbie. Thank you! I have been looking for something along those lines to get something started in my town in Canada.

  • Ian Turner


    Measuring pulmonary function wouldn’t be adequate because of factor interactions. Both activity and pulmonary function are independently affected by traffic, and they also both affect each other and are affected by obesity status. In order to make the distinction using statistical methods, one would have to find an instrument, a variable that affects one factor without itself being affected by either. Not sure what that would be, maybe proximity to chemical plants or traffic-controlled airborne particle count?



  • Ot seems to me that if the kids in the study had PFTs administered, and the ones who were obese were performing at or in excess of the published norms for their demographic profile, you could rule out pulmonary deficiency as a cause of the obesity.

  • Ian Turner

    BicyclesOnly, sure, but you could not draw the opposite conclusion.



  • An alternative explanation could be poverty. Poor people have a harder time affording healthy food; they’re also likely to live in food deserts. At the same time, high-traffic areas are often less desirable to live in, so poor people move in because the rents are lower; poor neighborhoods are also likelier to have highways and highway access roads shoved down their throats.


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