• Credit: Peter Arkle

America’s obsession with supersizing has ballooned from burgers, sodas, and lattes to SUVs, houses, and now freeways. Cities including Atlanta, Phoenix, and Washington, D.C., propose to widen some freeways to 24 lanes, or 400 feet—enough space for two 747s, side by side. The El Toro “Y” interchange in Orange County, Calif., already has 26 lanes. If this trend continues, you’ll need binoculars to find your exit.

How wide can freeways get before paving over entire cities? In the near future, these new “fatways” may actually become cities. A recent report by Arizona State University says U.S. population growth over the next few decades will gravitate toward two dozen superarteries, such as the nearly 300-mile “Sun Corridor” planned for Arizona. Stretching from Mexico through Phoenix and Tucson with development along the entire length, it will double the area’s population—a linear megalopolis.

But even subtle growth can have a dramatic impact. The environmental activist group Friends of the Earth estimates that just 10 miles of a new four-lane highway create the equivalent lifetime emissions of nearly 47,000 Hummers, and the public health implications are equally alarming. By overfeeding development, highways are fattening up America and Americans at the same time. A Georgia Tech study shows that every hour spent in a car each day increases the likelihood of obesity by 6 percent, while walkable, mixed-use neighborhoods decrease it by 7 percent, lowering the overall relative risk of obesity by 35 percent. The National Institutes of Health links obesity to decreased life expectancy, so more highways mean more sprawl, more fat, and shorter lives. Our roads are literally killing us.

Freeway expansion is intended to relieve congestion, but in fact it encourages more commuting and longer distances, so cities are trapped in a vicious cycle, enabling overdevelopment. The insidious sprawl of my hometown, Houston, was one of the reasons I left; it seemed impossible to do anything without a car, and “pedestrian” was a pejorative term. So imagine my shock when the city began reclaiming its inner-city neighborhoods and installed a light-rail transit system. If Houston can do it, any place can.

Beefing up an overstrained highway system is like force-feeding burgers to a heart-attack victim. A good remedy for both problems is simply to encourage more exercise: less driving, more walking. It doesn’t take much to start making communities fitter instead of fatter.