Sorry, we didn't build this place for you.

What’s the greatest threat to our planet? That’s the question that animates the short film Built to Last, which won top honors from the Congress for New Urbanism over the summer. You’ll have to watch it on YouTube to find out the answer.

But here’s a hint: it has to do with how we build our cities. We have for several generations built our most significant places on the cheap: homes, office buildings, churches, libraries and the infrastructure that connects them, all built on the low bid. The chief driving forces governing the character of our cities have been cheap energy and cheap ideas.

Cheap energy has primarily revealed itself in our transportation system, which evolved around low-price gasoline. Cheap ideas have been revealed in our corporate neglect of healthy design and healthy places. City planners, zoning officials, county commissioners all over the nation have allowed a landscape to evolve in which they don’t expect anyone to walk anywhere, ever.

Living our lives in the automobile has profound effects on our psyche and our political behavior, but the main impacts (literally) are on our bodies. The number one leading cause of death for Americans between the ages of one and twenty-four is car crashes. Automobiles, as a cause of death, have leap-frogged over every other source of child mortality, including birth defects, other kinds of accidents, cancer, and homicide.

Danger from automobiles can’t be escaped simply by avoiding cars. Because planners rarely “complete the street” by creating a transportation infrastructure that works for walkers, moms with strollers, bikers, cars, and public transport, pedestrian fatalities are high and rising. And there’s a racial disparity in the experience of death by car: Ethnic minorities and recent immigrants are more likely to be traveling on foot, and because they are trying to navigate environments that exclude walkers, they are many times more likely to be killed by cars than are white citizens.

Trying to live life without a car in an environment built mainly for automobiles has profound effects on the sense of social inclusion. The indignity of being a pedestrian is felt regularly by the poor and by ethnic minorities, and is felt only occasionally by affluent elites (who may encounter traffic on foot only while waiting for a car repair and looking for a coffee shop). I know mothers in my own neighborhood whose engagement with the outside world comes to a near halt when they give birth–instead of trying to battle traffic without sidewalks and safe crosswalks while pushing a stroller, they retreat to a world of television, cell phones, and indoor living.

The effect of the built environment on our bodies is not just felt through violent encounters with cars. Because we have created so many unwalkable, unlivable communities, Americans of all ages have grown heavier by degrees in the last 40 years. We are trained by the diet and exercise industries to think of the obesity epidemic as the result of individual gluttony or sloth, or to excuse it as a genetic predisposition. But America’s obesity problem will not be cured by diet or gym membership: the real problem is a lack of healthy environments that promote routine physical activity—walking as a way of life.

The body politic has also been harmed by our penchant for building environments for cars instead of people. A study last year from the Corporation for National and Community Service called “Volunteering in America” shows that in places where commuting times are burdensome, volunteerism takes a hit. There is only so much time  in the day– after fighting traffic for hours, one is little inclined to head back out to sort clothes or cook food at the rescue mission.

What is more worrying is the suggestion that long hours spent commuting works a change on our psyche. While you might think all those solitary hours in the car would make you crave social interaction, in fact the opposite appears to be true. According to the volunteering study “driving back and forth to work alone provides few opportunities to engage others and to build a positive social network.” And when people don’t spend time interacting with others, they begin to lose both the knack and desire for community-mindedness (part of what scientists have described as social capital).

I don’t know if that’s true, but I can’t help feeling a little disinclined to “love my neighbor as myself” after spending time on Atlanta’s downtown connector. Sociologist Robert Putnam calculates that for every additional 10 minutes of commute time in the car, there is a ten percent decline in social capital.

Not many of us living in the matrix can simply give up our cars. But faithful communities serving the poor are beginning to ask questions about our responsibility not just to green our lives and our houses, but also to create healthy places that foster community and justice, beachheads of livability and vitality that can begin to spread across the city landscape.

Flourish, my organization, has created a list of resources for learning more about the built environment, and what churches can do to make a difference.

A version of this article appeared in the January/February 2010 issue of PRISM magazine.