Weighing In on City Planning
Could smart urban design keep people fit and trim?
Lawrence Frank is no 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.
Metropolitan Atlanta, often called a poster child
for urban sprawl, has undergone rapid geographical expansion as its
population has burgeoned to about 5 million. Studies suggest that
urban sprawl contributes to physical inactivity and obesity.
"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,"
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
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
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."
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
TIGHT FIT. Densely built urban areas such as
Vancouver's downtown may encourage pedestrian traffic and promote
physical activity. In contrast, cities of low density, where people
depend on cars to get to stores and other facilities, seem to favor
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.
OBESITY CITY. Infrared satellite images show the
rapid geographical expansion of metropolitan Atlanta. Built-up areas,
such as roads and buildings, appear bluish-white against the red
backdrop of areas dominated by trees and plants.
In the second study, health psychologist James Sallis of San Diego
State University and his colleagues reported that residents of "high-walkability"
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 rates 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.
So far, the dozen strong studies that have probed the relationships
among the urban environment, people's activity, and obesity have all
agreed, says Ewing. "Sprawling places have heavier people," he says.
"There is evidence of an association between the built environment and
Cause or coincidence
The evidence for a relationship between physical activity, body weight,
and the environmental characteristics called urban form "looks
compelling," adds Ross Brownson, an epidemiologist at St. Louis University
School of Public Health in Missouri.
But Brownson, Ewing, and others caution that these associations don't
prove that sprawl causes laziness or weight gain. Most of the studies
provide only a snapshot of different people at a single time. Such studies
can't prove that living amid sprawl leads to inactivity; it may also be
that inactive people choose to inhabit areas where driving is the easiest
way to get around.
In other words, people with different health habits and different
propensities to gain weight may sort themselves into different kinds of
That's what Turner suggests is going on. 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
Turner's team analyzed data collected over 6 years on more than 5,000
young adults living across the United States. Most of the volunteers moved
at least once during the study. The researchers compared individuals'
weights before and after they moved between communities with different
degrees of sprawl.
To measure sprawl, they used satellite images to calculate the average
distance between residential buildings. They also determined the average
density of nonresidential establishments such as churches and shops in
each volunteer's zip code.
"We're estimating the effect [of sprawl on weight] to be zero or very
close to zero," Turner says. Any weight gain attributable to sprawl, he
says, is at most "a couple of ounces."
The authors released the study as a working paper on Oct. 30, 2006.
Other researchers challenge some of the study's analytical methods,
particularly the way in which Turner's team assessed sprawl and mixed use.
For example, Sallis says, "They assumed that [churches and retail
businesses] were equally dispersed around the zip code." The study may
therefore have inaccurately estimated volunteers' access to walkable
destinations, he says.
Sallis also argues that it could take many years for significant weight
gain to develop after a person moves between dissimilar neighborhoods.
Moreover, the study didn't assess whether volunteers' degree of physical
activity changed when they moved, a measure that would hint at impending
changes in weight.
Still, Sallis says, Turner's longitudinal approach to the issue is
"definitely an advance. We've been wanting studies like this for some
Ewing has also completed a prospective study using a similar set of
data, but he declined to discuss his results with Science News
before the study's publication.
Obesity is not the urban environment's only—nor even necessarily its
most likely—potential health effect, says physician Deborah Cohen, a
health researcher at the RAND Corporation in Santa Monica, Calif. If a
neighborhood's design were to make people less active, they might eat less
to avoid obesity but still miss out on other health benefits of physical
activity, notes Cohen.
"Physical activity is independently important for health, [and] urban
form is important for physical activity," she says.
In 2004, Cohen and Roland Sturm of RAND asked more than 8,000 residents
of 38 U.S. communities to list their health problems. The researchers also
assessed the degree of sprawl in each resident's community.
"People reported more complaints—more health problems—when they lived
in more sprawling areas," Cohen says. The excess of physical problems such
as arthritis linked to sprawl was comparable to the change that would
occur if the entire population suddenly aged by 4 years, Cohen and Sturm
Setting and sorting
Frank's latest findings 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.
THE DISCONNECT. A community's so-called network
efficiency influences its walkability. In an efficient network, such
as in the gridlike neighborhood at left, pedestrians can walk
relatively directly between any two points. The maze of cul-de-sacs
at right forms an inefficient network.
His study, he says, "demonstrates that both preferences and the
neighborhood in which people live impact their behavior." He described the
findings at a conference in Atlanta on Jan. 19 and reports them in an
upcoming Social Science and Medicine.
The people most at the mercy of sprawl, Ewing suggests, are those who
have limited access to healthy foods and who don't recognize the
importance of fitness.
Children are another group that could be disproportionately affected by
urban design, Frank says.
In two recent studies, Cohen and her collaborators examined the
relationship between adolescent girls' physical activity and specific
aspects of the urban environment. Girls who live near parks and
recreational facilities are more physically active than those whose
neighborhoods contain no such spaces, the researchers found.
They selected a middle school in each of six metropolitan areas
throughout the country. From among the female students attending the
schools, the team randomly selected 1,556 sixth graders.
In one study, the researchers used maps and government records to
locate public parks. On average, 3.5 parks lay within a 1-mile radius of
each volunteer's home. That figure varied from about six parks in
Minneapolis to about one park in Tucson.
The researchers outfitted the girls with pedometerlike devices called
accelerometers, which record motion and can be used to measure the
intensity of physical activity. Each volunteer wore her accelerometer for
6 consecutive days. During that time, the girls performed, on average, the
metabolic equivalent of 611 minutes of vigorous physical activity.
The researchers conservatively estimated that each park within a
half-mile of home contributed an extra 17.2 minutes of vigorous activity
per girl over the course of the study. The team reports its findings in
the November 2006 Pediatrics.
"Neighborhood parks are particularly important for adolescents who are
too young to drive," says Diane Catellier, a statistician at the
University of North Carolina at Chapel Hill who collaborated with Cohen on
In the other study, reported in a 2006 supplement to the Journal of
Physical Activity and Health, Cohen's team used data on the same girls
to show that living in proximity to one's school is also associated with
increased levels of physical activity.
"The overarching message is that the built environment is an enabler or
a disabler of active transportation—of walking," Frank says.
Cohen, D.A., et al. 2006. Public parks and
physical activity among adolescent girls. Pediatrics
118(November):e1381-e1389. Available at
Cohen, D.A., et al. 2006. Proximity to school
and physical activity among middle school girls: The trial of activity for
adolescent girls study. Journal of Physical Activity and Health
3(Suppl. 1):S129-S138. Available at
Eid, J., et al . . . and M.A. Turner.
Preprint. Fat City: Questioning the relationship between urban sprawl and
obesity. Working paper. Available at
Ewing, R., et al. 2003. Relationship between
urban sprawl and physical activity, obesity, and morbidity. American
Journal of Health Promotion 18(September/October):47-57. Available at
Frank, L.D., et al. 2004. Obesity
relationships with community design, physical activity, and time spent in
cars. American Journal of Preventive Medicine 27(August):87-96.
Frank, L.D., et al. In press. Social
Science and Medicine.
Saelens, B.E., J.F. Sallis, et al. 2003.
Neighborhood-based differences in physical activity: An environment scale
evaluation. American Journal of Public Health.
93(September):1552-1558. Available at
Sturm, R., and D.A. Cohen. 2004. Suburban sprawl and
physical and mental health. Public Health 118(October):488-496.
Abstract available at
Ross C. Brownson
Department of Community Health and Prevention Research Center
Saint Louis University School of Public Health
St. Louis, MO 63104
Diane J. Catellier
University of North Carolina, Chapel Hill
School of Public Health
137 E. Franklin Street, Suite 203
Chapel Hill, NC 27599
Deborah A. Cohen
1700 Main Street
Santa Monica, CA 90401
National Center for Smart Growth
University of Maryland, College Park
1112J Preinkert Field House
College Park, MD 20742
Lawrence D. Frank
School of Community and Regional Planning
University of British Columbia
1933 West Mall Annex #231
Vancouver, British Columbia V6T 1Z2
James F. Sallis
Department of Psychology
San Diego State University
3900 5th Avenue, Suite 310
San Diego, CA 92103
Department of Economics
University of Toronto
150 Saint George Street
Toronto, Ontario M5S 3G7