Atlanta ? Spending more time behind the wheel — and less time walking — is adding inches to waistlines and contributing to the nation’s obesity epidemic, a study concludes.

The survey of 10,500 metro Atlanta residents found that for every extra 30 minutes commuters drove each day, they had a 3 percent greater chance of being obese than their peers who drove less.

The survey also found that people who lived within walking distance of shops — less than a half mile — were 7 percent less likely to be obese than their counterparts who had to drive.

“The more driving you do means you’re going to weigh more — the more walking means you’re going to weigh less,” said Lawrence Frank, associate professor at the University of British Columbia who oversaw the study at Georgia Tech.

That much seems obvious, but researchers were surprised to discover that how much time a person spent driving had a greater effect on whether a person was obese than other factors such as income, education, gender or ethnicity.

About 91 percent of the people surveyed said they didn’t walk to destinations. Many spent more than an hour each day in their cars.

The study is one of the first to look at the link between the environment and obesity, said Kelly Brownell, chairman of Yale University’s psychology department and director of its Center for Eating and Weight Disorders.

In the study, researchers tracked participants’ travel behavior and measured their height and weight from 2000 to 2002.

The study focused on Atlanta, but Frank said the city was not alone.

Weekend motorists make their way past the Interstate 285 connector outside of Atlanta. A new study shows that for every extra 30 minutes commuters drive each day, they have a 3 percent greater chance of being obese than people who drive less.

“Most regions look very similar to Atlanta; anything that’s built after World War II is pretty much auto-oriented,” he said. “We need to start to look at the way we’re designing our communities … the collective impact of having to drive everywhere is becoming really large.”