At the moment, the world—including Americans, the world's heaviest users of fossil fuels—have what may turn out to be one of the most important, and shortest, windows of opportunity in history. For a time that may be all too brief, the urgent need of our health (for more physical movement) and the urgent need of our environment (for less fossil fuel combustion) are in harmony, not in conflict.

We need to get out of our cars and walk, to save our health and our climate. And a little change in that direction might make more difference than we think.

Here's a suggestion for lopping off an increment of pollution and lowering cholesterol, warding off diabetes and improving the health of a population facing an obesity epidemic: let's leave the car in the garage when we're making trips of a half-mile or less without passengers or cargo. Even if we get back into the car when the weather's bad or we're schlepping groceries or soccer equipment, we're still saving a lot of trips.

It's not just a matter of pounds shed and gas saved (though that will be more than we think, because in the case of very short trips, the additional gas wasted in the search for parking spaces may nearly equal that used for the trip itself). Getting in the habit of ruling the car out for short trips will lead to greater things. The half-mile will become three quarters, then a mile, because our bodies prefer movement.

In Brattleboro, one of many communities across the country which have signed on to the Cities for Climate Protection program, part of that program involved an event called the Curb Your Car Challenge. "We actually challenged people to record their trips and try to reduce the number of them," says the town's CCP director, Paul Cameron, who lives in town and walks about three-quarters of a mile to work. Cameron adds that the event was "quite successful," and that though he hasn't seen a measurable increase in the number of people walking, he has seen more people biking instead of driving in Brattleboro.

By itself, walking those half-mile trips won't solve the world's energy problems. But it will help us get into habits that will ease our passage to a future with less oil. As reasons for using less petroleum become more pressing, our energy future will become a mosaic of increments—incremental, varied sources, incremental savings. It's hard to quantify how much fuel walking (or biking) short distances could save, but figures from the Federal Highway Administration suggest that, in an age when increments are important, the savings could be significant.

As of 2004, for example, adult Americans, who average about four trips away from home per day, were making 49 percent of all trips of half a mile or less by car (school-age children walk more). Pinning down the numbers of short trips isn't easy, but according to one estimate, 123 million car trips a day or more are "short enough to have been made on foot."

I grew up in a small town in Florida in a family that didn't have a car. Except when I wanted to cover the five miles to the beach, I didn't miss one. Granted, we had an intown location, a forgiving climate and a negligible crime rate, and in the interests of full disclosure I admit that my aunt, who had a car, took us for a big stock-up trip to the grocery store about every six weeks. But for most purposes, life in the minority of the carless (even now about a tenth of Americans own no car) wasn't very hard. For my divorced working mother there were no car payments, no insurance premiums, no fear of being cheated at the garage.

And I wasn't so different from other children. Back then (the 1950s: think Dwight Eisenhower, Dinah Shore and banks that didn't eat up your deposits with fees), most families had only one car, which usually went to work with Dad. So lots of kids walked lots of places. The conventional assumption about destinations within "walking distance" was that you walked to them.

But making walking the preferred way of accomplishing the basics of living takes community planning as well as determination on the parts of pedestrians, says Susan Berry, coordinator of the Upper Valley Rideshare program in Vermont and New Hampshire.

Peripheral parking instead of downtown garages, and retail mixes that place basic services, from banking to food shopping, within walking distance of town centers, are important, says Berry. And, she adds, "If you're going to extend growth out, be sure there are sidewalks, bike lanes." The result could restore a long-lost balance between our air quality, our energy use and our health.•