UBC urban-planning professor Larry Frank has been on the front lines of the sprawl debate. And the current issue of Science News has a fine cover-page story on the controversy.
Larry did much of his research in Atlanta, Georgia, where he lived for many years. After moving to Vancouver, he personally experienced the consequences of the city’s different design.

The glaring difference between the two cities’ landscapes figures in Frank’s professional life as well as in his personal one….
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.

The story provides good background on the “sorting versus causation” debate. The first studies (only four years ago) linked sprawl and obesity:

Residents of sprawling cities and counties tended to weigh more, walk less, and have higher blood pressure than did people living in compact communities …
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.

Then came the counter-arguments.

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.”
Turner conducted a study that tracked people over time, as some of them moved from one neighborhood to another. He and his collaborators found no change in weight associated with moving from a sprawling locale to a dense one, or vice versa.
“We’re the only ones that have tried to distinguish between causation and sorting … and we find that it’s sorting,” he says. “The available facts do not support the conclusion that sprawling neighborhoods cause weight gain.”

Frank and others involved in the original research were always aware of the sorting-causation distinction. And now their latest work “could split the ideological difference.”

By surveying people in a variety of neighborhoods, he learned that people who are less inclined to be active tend to live in less pedestrian-friendly locales—evidence that people are sorting themselves. But he also found that, no matter how much people like or dislike being active, they are more active when they live in compact, walkable areas than when they live in sprawling neighborhoods.

Larry has also made the point to me: So what if people sort themselves? We need to offer people more opportunities to live in the kind of neighbourhood where they can walk if they choose. Too often our urban design discourages physical activity regardless of people’s motivations.

“The overarching message is that the built environment is an enabler or a disabler of active transportation—of walking,” Frank says.

Full story here.


  1. What about the children of the sorters? Can we glean the difference between sorting and causation if we look at them? Are city kids more or less likely to be obese, relative to adults?

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