Weighing in on city planning: could smart urban design keep people fit and trim?

Science News,  Jan 20, 2007  

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Lawrence Frank is couch potato. Taking full advantage of his city s compact design, the Vancouver, British Columbia, resident often bikes to work and walks to stores, restaurants, and museums. That activity helps him stay fit and trim. But Frank hasn't always found his penchant for self-propulsion to be practical. He previously lived in Atlanta, where the city's sprawling layout thwarted his desire to be physically active as he went about his daily business.

"There was not much to walk to," says Frank, a professor of urban planning at the University of British Columbia. For example, he recalls that there was only one decent restaurant within walking distance of his old home. Many restaurants and other businesses in Atlanta cluster in strip malls that stand apart from residential areas.

In Vancouver, by contrast, Frank's neighborhood contains dozens of eateries, and he often strolls to and from dinner. "I'm more active here," he says.

The glaring difference between the two cities' landscapes figures in Frank's professional life as well as in his personal one. Frank is part of an emerging area of cross-disciplinary science that's examining the relationship between the shapes of our cities and the shapes of our bodies.

He and other researchers have evidence that associates health problems with urban sprawl, a loose term for humanmade landscapes characterized by a low density of buildings, dependence on automobiles, and a separation of residential and commercial areas. Frank proposes that sprawl discourages physical activity, but some researchers suggest that people who don't care to exercise choose suburban life. Besides working to settle that disagreement, researchers are looking at facets of urban design that may shortchange health.

As scientists investigate the relationship between sprawl and obesity, a compact style of city development sometimes called smart growth might become a tool in the fight for the nation's health. However, University of Toronto economist Matthew Turner charges that "a lot of people out there don't like urban sprawl, and those people are trying to hijack the obesity epidemic to further the smart-growth agenda [and] change how cities look."

STUDYING SPREAD For decades, housing and population growth in U.S. suburban areas have outpaced those in city centers. Shifts in commuting patterns reflect the trend toward people residing at a sizable distance from where they work, shop, and play. According to U.S. Census data, the average commute lengthened from 22.4 minutes to 25.1 minutes between 1990 and 2000, and the proportion of workers walking or biking to work dropped by one-quarter.

A few communities buck the national trend. For example, Frank says, "there is a great deal of new development in Atlanta that is walkable."

"That said, the overall trend is not in this direction in that region or most others," he adds. Even "Vancouver is embarking on a massive road-building program that threatens [to create] sprawl in the developing parts of this region"

In September 2003, two major studies linked sprawl and obesity. Since those reports, researchers in fields as disparate as epidemiology and economics have generated a spate of similarly themed studies.

In the first of the 2003 reports, researchers analyzed data from a nationwide survey in which each of some 200,000 people reported his or her residential address, physical activity, body mass, height, and other health variables. Residents of sprawling cities and counties tended to weigh more, walk less, and have higher blood pressure than did people living in compact communities, concluded urban planner Reid Ewing and his colleagues at the University of Maryland at College Park's National Center for Smart Growth Research and Education.

In the second study, health psychologist James Sallis of San Diego State University and his colleagues reported that residents of "highwalkability" neighborhoods, which have closely packed residences and a mix of housing and businesses, tended to walk more and were less likely to be obese than residents of low-walkability neighborhoods.

In 2004, Frank and his colleagues produced additional connections among urban form, activity, and obesity. The data on more than 10,500 people in the Atlanta area indicated that the more time a person spends in a car, the more obese he or she tends to be. But the more time people spend walking, the less obese they are.

Frank's team, like the other groups, found that areas with interspersed homes, shops, and offices had fewer obese residents than did homogeneous residential areas whose residents were of a similar age, income, and education. Furthermore, neighborhoods with greater residential density and street plans that facilitate walking from place to place showed below-average rate of obesity.

The magnitude of the effect wasn't trivial: A typical white male living in a compact, mixed-use community weighs about 4.5 kilograms (10 pounds) less than a similar man in a diffuse subdivision containing nothing but homes, Frank and his colleagues reported.