When Susan Handy moved to Davis, Calif., in 2002, she immediately bought a commuting vehicle: a wheeled trailer, for toting her kids behind her bike. Handy, an environmental policy analyst at the University of California, and her husband frequently pedal to work, with two preschoolers in tow. Among locals, their commute is common. Fifty miles of bike lanes ribbon Davis, which is only about 10.5 square miles in area. Handy calls Davis a small town that really works.

City planners, health researchers and local leaders want more U.S. communities to really work--and to that end, they have begun retrofitting the country, from Atlanta to Sacramento. Inspired by a new urbanism that celebrates neighborhoods and alarmed by health problems--particularly childhood obesity--these trailblazers are building paths, sidewalks and other architectural features while promoting policies and behaviors that get people moving.

They have plenty to do. America's metropolitan landscape is a fractured network of residential and industrial buildings, haphazardly decorated with green space. To get around in their built environment, or human-made surroundings, members of the average American household collectively logged more than 32,000 miles of car travel in 2001. According to National Household Travel Survey data, only 15 percent of children in the U.S. walk or bike to school--a 35 percent drop from three decades ago. At the same time, kids now spend an average of 44 hours a week sitting in front of a television, computer screen or other video monitor, according to a 2005 Kaiser Family Foundation study. Over the past five years, the study concludes, this Generation M (for media) has increased its total exposure by more than an hour each day, mostly by multitasking with different forms at once.

Our built environment is a recipe for health problems, from obesity to asthma to depression, says Richard Jackson, an adjunct professor of environmental health at the University of California, Berkeley. Poor urban design has a distinct impact. Childhood obesity, in particular, has become epidemic. Nearly a fifth of all children and adolescents in the U.S.--more than 12 million--are now overweight, according to the CDC's National Center for Health Statistics. Can the U.S. redesign itself for a healthier future?

Trails to Fitness

Today's built environments reflect decades of urban planning with a few consistent themes--cars and zoning, among them. The advent of America's car culture in the 1950s inspired suburbs that sprawl, Handy points out. Reinforcing this trend, urban zoning requirements have frequently separated industrial or commercial settings and residential neighborhoods--partly in the interest of public health, to ensure that most homeowners do not live near polluting factories.

But this blueprint currently looks less benign. Pollution from nonfactory sources, such as smog from car tailpipes and lawn equipment, still fouls the air and contributes to asthma. Idle hours in the car spent traveling between residential and commercial destinations add up to inactivity. Even those who prefer to bike or walk often confront crowded roads and hectic intersections.

Rather than simply accepting this modern metropolis, early built-environment mavericks pushed for local change. On a sunny day in 1991, for instance, three cycling buddies in sprawling Atlanta together lamented the city's polluted air and lack of bike trails. Then they got busy. The trio created the PATH foundation, a nonprofit whose mission is to develop a system of linked trails throughout metropolitan Atlanta.

Sixteen years later the PATH foundation has built 110 miles of trails in and around the city, through wetlands and nature preserves, along highways and across neighborhoods. The longest trail, dubbed the Silver Comet, stretches 57 miles from Atlanta to the Alabama state line. Built with a plan that combines public and private financing, all the trails are 12 feet wide, made of concrete and lined with maintained green space. PATH's executive director, Ed McBrayer, calls the trails linear parks.

We intend for all the trails to eventually link, like a transportation system, so people can use them to get to work, school, the gym and church, McBrayer says. We're always building: two miles there and one mile here, on abandoned railroad tracks, wherever we have the money and the political will. Although data on how the trails are used are limited, it is known that they inspire some exercise: in a January 2007 study by PATH foundation staff and Emory University researchers, sponsored by Georgia Healthcare Foundation, a third of 315 trail users surveyed at Davidson-Arabia Mountain Nature Preserve said that most of their weekly physical activity has involved the trails.

Similarly, a network of trails in the college town of Columbia, Mo., was born when educational technologist Ian Thomas and some friends calculated that the town of 75,000 included at least 60 residential streets lacking sidewalks. They founded the PedNet Coalition, now directed by Thomas, to lobby policymakers for pedestrian-friendly improvements and to promote activity to Columbia residents.

In 2004 PedNet convinced Columbia's city council to revise its street design standards, adding or widening sidewalks, bike lanes and mixed-use paths. Those changes, in turn, helped the city win a 25-million grant from the Federal Highway Administration to build a comprehensive cycling and walking network. As part of the grant, Columbia will document how its efforts boost bicycling and walking, reduce traffic and energy use, and promote better health and a cleaner environment.

In fact, major changes in federal transportation policy are boosting built-environment projects nationwide. Spurred by local constituencies, lawmakers in 1991 and 1998 formally added bicycling and walking to transportation planning. As a result, bicycle and pedestrian projects--from sidewalks to bicycle lanes, trails and parking--now qualify for federal funds once dedicated exclusively to highways. Today states and metro areas are legally required to consider bicyclists and pedestrians in transportation plans. What's more, a 2005 federal transportation bill allocated an additional 612 million for a new national Safe Routes to School program, requiring all states to hire a coordinator to administer funds to communities for new bike lanes, pathways, sidewalks, and education and promotion campaigns in elementary and middle schools.

Built-environment advocates agree that promotion--from generating political will to inspiring individual choice--is critical to their cause. Thomas points to school location as one example. Because public schools are not seen as high priority, they are underfunded and thus buy the cheapest land available, on the edge of town, Thomas explains. How do you get your kids there? You have to drive.

Even the support of neighbors isn't guaranteed. In Atlanta, McBrayer was surprised to discover that culture--not just cash--was an obstacle. I initially assumed everyone wanted to be connected, McBrayer recalls. And that's not true. There are class and race issues, privacy issues and people who don't want things to change.

Adding to the challenge, Americans plainly enjoy their cars. In a 2005 study sponsored by the Southwest Region University Transportation Center, Handy and her colleagues interviewed Texas drivers to determine their routes to local destinations. They asked the question: How much of driving is determined by choice, rather than need? The answer: a significant amount. The study found that people often take extra trips, choose longer routes, pick more distant destinations and opt to drive rather than walk or bike.

Exercise physiologist Russell Pate of the University of South Carolina sees this tendency in his own community. I live in a safe, relatively low traffic neighborhood with sidewalks that lead to a local elementary school, Pate says. Every morning there's a line of SUVs half a mile long dropping off kids. The built environment is not the barrier there.

Desperation Grows

Yet as the health-environment connection evolves into a national issue, foundations are stepping up to the challenge. This year the Robert Wood Johnson Foundation (RWJF), the largest U.S. philanthropy devoted to health, committed 500 million to fighting childhood obesity. Those funds will in part support three existing RWJF organizations--Active Living by Design, Active Living Research and Leadership for Healthy Communities--that seek to change policy, the environment and behavior to boost physical activity.

There's almost a desperation around the country to do something about childhood obesity, says Active Living Research program director James Sallis, who is also a psychologist at San Diego State University. Active Living Research, in particular, is working to assemble evidence that the right built environments boost physical activity and improve health. Increasingly, we plan to focus on funding peer-reviewed research that documents the most promising ways to reduce childhood obesity, Sallis says.

In one of his own studies, published this past March in the American Journal of Health Promotion, Sallis collaborated with urban design specialist Lawrence Frank of the University of British Columbia and others to link Atlanta's built environment with walking patterns in the city. Surveying more than 3,000 children and their parents, the researchers found that kids aged 12 to 15 were three times more likely to walk half a mile a day if a park, store or other popular destination were located within about 0.62 mile (one kilometer) of their homes. Overall, the team reported, children and families living in a mixed-use community--which offers destinations within walking distance--walk significantly more.

Walking half a mile may not sound like much exercise, but Pate puts it into perspective. He notes that preventing excess weight gain is likely to be easier than losing pounds. Furthermore, he says, most people pack on pounds gradually, because their day-to-day consumption of unburned calories is relatively small. Over time, for instance, 50 extra calories a day can cause someone to become overweight. And a 10-year-old can burn more than 50 calories just walking to or from school or the park on a daily basis, Pate points out.

Still, skeptics question how much sprawl is to blame for obesity. In a 2003 online editorial, the Heritage Foundation, a conservative think tank in Washington, D.C., argued that without more evidence, public policy should not require denser, mixed-use community designs. The foundation emphasized that data from the CDC on 445 counties showed few overall weight differences between communities designed differently. For the country as a whole and comparing citizen weight in the 25 counties at either extreme of sprawl and compactness, 19.2 percent of residents in the least sprawling communities were obese, while 21.2 percent in the most sprawling were obese, the editorial noted, calling such differences trivial.

Sallis has heard that argument before. Most people would agree that there is not going to be a single solution to childhood obesity, he responds. We have to pursue many solutions. We have to make it harder to drive and easier to bike. We have to make it easier to find affordable, healthy food and harder to find junk food. We have to make it easier for kids to be active at school and after school. Obesity is a difficult problem to fix, but it's certainly possible--and environment is a factor.

In particular, Sallis continues, minority and low-income communities need new solutions. Studies have shown that these neighborhoods, on average, include fewer parks, more fast food outlets and more crime than affluent or Caucasian neighborhoods. Against this backdrop, these communities frequently suffer higher rates of obesity. Active Living Research plans to increase its support for reviews of these high-risk populations, Sallis says.

Other investigators are evaluating classic neighborhood designs. In northern California, Handy and her colleagues are studying cul-de-sacs, those horseshoe-shaped streets that typically dead-end at middle-class family homes dressed with basketball hoops, soccer nets and other sports paraphernalia. Seeking more connectivity, partly to promote walking and biking, city planners are increasingly outlawing cul-de-sacs in favor of streets laid out in a grid pattern.

But in a study presented at an Active Living Research Conference this past February, Handy's team reported another side to the story. Across 27 households in Woodland, Calif., 75 percent of children living in cul-de-sacs reported being highly active outdoors, versus 55 percent of those residing on through streets. In a related survey of 1,672 parents, children ages five to 12 living in cul-de-sacs played outside more than four times in a given week, at least once more than those on through streets. What's the best neighborhood design for kids, and what's the best for adults? Handy asks. The answer may not be simple.

Elusive or not, the built environment is likely to become an even hotter topic of debate in years to come. For proof, Jackson points to his experience at U.C. Berkeley. My students are as intensely invested in these issues as students were 30 years ago in the Vietnam War, he says. We're going to retrofit communities to improve our health--and to improve our environment. These concerns are here to stay.