Why Cul-de-Sacs Are Bad for Your Health

The Eye
Slate’s design blog.
Dec. 10 2013 9:00 AM

Why Cul-de-Sacs Are Bad for Your Health

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A cul-de-sac in Austin, Texas

Coutesy of The Muuj via Flickr

Award-winning Canadian journalist Charles Montgomery's fascinating new book Happy City: Transforming Our Lives Through Urban Design examines how lessons from psychology, neuroscience, and design can help us fix broken cities and improve our quality of life in an increasingly urban-centered world. Here at the Eye, Montgomery shares an excerpt from the book.

Of every 100 American commuters, five take public transit, three walk, and only one rides a bicycle to work or school. If walking and cycling are so pleasurable, why don’t more people choose to cycle or walk to work? Why do most people fail to walk even the 10,000 daily steps needed to stay healthy? Why do we avoid public transit?

I was naive enough to ask that question of a fellow diner I met in the food court of the bunkerlike Peachtree Center in downtown Atlanta. Her name was Lucy. She had driven her car in that morning from Clayton County (a freeway journey of about 15 miles), pulled into a parking deck, followed a skyway a few dozen paces to an elevator, and then a few more to her desk. Trip time: about half an hour. Total footsteps: maybe 300. She flashed me a broad smile.

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“Honey, we don’t walk in Atlanta,” Lucy told me. “We all drive here. I can’t say why. I guess we’re just lazy.”

Lazy? The theory doesn’t stand up. Lucy’s own commute was proof. She could not have made it to work any other way. Suburban Clayton County suspended bus service in 2010. (The service had carried 2 million riders in 2009 before it was shut down.)

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Nobody walks in Atlanta.

Courtesy of Steve Hardy via Flickr

No, the answer to the mobility conundrum lies in the intersection between psychology and design. We are pushed and pulled according to the systems in which we find ourselves, and certain geometries ensure that none of us are as free as we might think.

Consider Atlanta. The average working adult in Atlanta’s suburbs now drives 44 miles a day. (That’s 72 minutes a day behind the wheel, just getting to work and back.) Ninety-four percent of Atlantans commute by car. They spend more on gas than anyone else in the country. In a study of more than 8,000 households, investigators from the Georgia Institute of Technology led by Lawrence Frank discovered that people’s environments were shaping their travel behavior and their bodies. They could actually predict how fat people were by where they lived in the city.

Frank found that a white male living in Midtown, a lively district near Atlanta’s downtown, was likely to weigh 10 pounds less than his identical twin living out in a place like, say, Mableton, in the cul-de-sac archipelago that surrounds Atlanta, simply because the Midtowner would be twice as likely to get enough exercise every day.

Here’s how their neighborhoods engineer their travel behavior:

Midtown was laid out long before the dispersalists got their hands on the city. It exhibits the convenient geometry of the streetcar neighborhood even though its streetcars disappeared in 1949. Housing, offices, and retail space are all sprinkled relatively close together on a latticelike street grid. A quart of milk or a bar or a downtown-bound bus are never more than a few blocks away. It is easy for people to walk to shops, services, or MARTA, the city’s limited rapid transit system, so that’s what they do.

But in suburbs like Mableton, residential lots are huge, roads are wide and meandering, and stores are typically concentrated in faraway shopping plazas surrounded by parking lots. Six out of every 10 Atlantans told Frank’s team that they couldn’t walk to nearby shops and services or to a public bus stop. Road geometry was partly to blame. Frank and others have found that that iconic suburban innovation—the cul-de-sac—has become part of a backfiring behavioral system.

When designers try to maximize the number of cul-de-sacs in an area, they create a dendritic—or treelike—system of roads that feeds all their traffic into a few main branches. The system makes just about every destination farther away because it eliminates the most direct routes between them. Connectivity counts: More intersections mean more walking, and more disconnected cul-de-sacs mean more driving. People who live in neighborhoods with latticeworklike streets actually drive 26 percent fewer miles than people in the cul-de-sac forest.

The diagram below helps illustrate how a white male living in Midtown (left), near Atlanta’s downtown, is likely to weigh 10 pounds less than his identical twin living near Mableton (right), a sprawling suburb. This is partly owing to road geometry and land-use mix: a 10-minute walk from a home amid the traditional grid in Midtown will get you to grocery stores, schools, bus stops, cafés, a bank, and the glorious lawns of Piedmont Park. But the spread-out and homogeneous system of Mableton pushes destinations beyond walking range, which means residents are likely to drive whether they like driving or not. (Each bullet represents a school, church, grocery store, dry cleaner, bank, day-care center, police station, transit stop, or hospital. If restaurants, cafés, bars, and other services were included, the Mableton map would not change, but the Midtown map would be sprayed with dozens more bullets.) 

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How street shapes can affect our own shapes

Courtesy of Erick Villagomez, Metis Design Build

Our responses to distance are quite predictable. Most of us will walk to a corner store rather than climb in and out of the car if it’s less than a five-minute walk—about a quarter mile—away. We won’t walk more than five minutes to a bus stop, but we will walk 10 to a light-rail or subway station, partly because most of us perceive rail service to be faster, more predictable, and more comfortable. This is the geometry perfected by streetcar city developers a century ago. It’s now being rediscovered by planners who find that simply introducing regular high-quality light-rail service can alter the habits—and the health—of people nearby. Less than a year after the LYNX commuter light-rail line was installed in Charlotte, N.C., people living near the line had started walking an extra 1.2 miles every day because the system changed their daily calculus. People who switched to the LYNX for their commute lost an average of 6½ pounds during that time.

Kids move by a similar calculus. Frank found that if there is a park or some kind of store within a half mile of their home, school-age youth are more than twice as likely to walk. If destinations are farther, they wait for a parental chauffeur. Think of the implications: a community with one central mega-sports complex with several baseball diamonds and soccer fields can actually be bad for children’s health if it replaces small parks scattered every few blocks. In the finer-grained community, instead of begging Mom for a ride to a league game, a teenager might find it easier to organize her own game at the local park.

“The way we organize most cities actually encourages individuals to make choices that make everyone’s life harder,” Frank told me. “The system fails because it promises rewards for irrational behavior.”

Put simply, most people do not walk in American cities because cities have designed destinations out of reach. But they have also corroded the experience of walking. Road engineers have not even bothered to build sidewalks in many Atlanta suburbs. Try a Google search for directions near, say, Somerset Road in Mableton, and the map engine will offer a warning you would not expect in a first-world city: “Use caution—This route may be missing sidewalks or pedestrian paths.”

Aesthetics matter. We walk farther when streets feel safe and interesting. People who live in central New York or London typically walk between a third to a half mile to go shopping. That’s a four- to 10-minute stroll. Even in Montreal, with its freezing winters and sweat-soaked summers, people reported walking about a third of a mile (six to eight minutes) between shops, bags in tow. The numbers are almost as high for people arriving at enclosed shopping malls, which mimic the downtown experience, at least once you’re in the building. But dump us in a vast parking lot surrounded by big-box outlets, and our inclination to walk evaporates. Even when people are equipped with shopping carts, they won’t endure so much as the three-minute stroll between retailers. Researchers observed that a third of the shoppers at one Canadian power center (the north-of-the-border term for a big shopping outlet) actually parked their cars three or more times during one visit. They just hated trudging across the asphalt desert. It felt ugly, uncomfortable, and unsafe.

You might speculate that these studies merely demonstrate the city’s power to sort people by their preferences: Maybe Manhattanites walk because they are walkers, while Atlanta’s big-lot suburbanites and Canada’s power-center pilgrims drive because they prefer the air-conditioned comfort and storage capacity of the family minivan. In other words, just because urban designs correlate with travel behavior, it doesn’t mean they cause it.

This view is partly true. People do self-sort in cities. In Atlanta, for example, Frank found that people who said they preferred to live in car-dependent neighborhoods tended to drive pretty much everywhere, no matter where they lived. Not surprisingly, people who both liked and lived in lively, walkable places drove less and walked more. But the suburbs were full of people who wished they could walk places but couldn’t. Nearly a third of people living in Atlanta’s car-dependent sprawl wished they lived in a walkable neighborhood, but they were mostly out of luck because Atlanta had gone nearly half a century without building such places.

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Atlantic Station in Atlanta

Courtesy of Chris Yunker via Flickr

When Atlanta builds differently, people do change their movements. Proof sits on the edge of a tangled freeway interchange three miles north of the city center, where the 138-acre site of a former steel mill has been redeveloped into a dense mix of offices, apartments, retail stores, small parks, and theaters. Despite the fact that much of Atlantic Station, as it is known, sits atop a three-level parking garage, people who have moved there since 2005 have shaved a third of the miles off their driving. Instead, they walk, because some of their destinations have suddenly fallen within the range of a pleasant sidewalk stroll.

Excerpted from Happy City: Transforming Our Lives Through Urban Design by Charles Montgomery, published in November 2013 by Farrar, Straus and Giroux, LLC. Copyright © 2013 by Charles Montgomery. All rights reserved.

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