Taking public transportation whenever possible may have an added benefit of helping people lose weight, say researchers at Drexel University. Though it may not come as a total surprise, the study provides some nice evidence that using the car less and walking more may have some real, measureable health benefits.

To study the idea, John M. MacDonald and his team surveyed residents of Charlotte, NC both before and after the city’s light rail transit (LRT) was constructed. The participants answered questions about their weight, exercise habits, how much they’d planned to use the LRT, and how much they actually used it.

Most impressive was the fact that people who took the LRT were 81% less likely than drivers to become obese.

The researchers found that over a 12-18 month follow-up period, the participants’ body mass indexes (BMIs) fell by an average of 1.18 kg/m2 after they switched to the public transit. This is roughly equivalent to a 5’5” person losing about 6.45 pounds. Most impressive was the fact that people who took the LRT were 81% less likely than drivers to become obese.

In the journal’s press release, MacDonald says that “[t]he built environment can constrain or facilitate physical activity. Understanding ways to encourage greater use of local environments for physical activity offers some hope for reducing the growth in the prevalence of obesity.”

So if your city offers public transportation, take up the offer – not only is it good for the environment and may reduce your stress level (those rush-hour traffic jams aren’t good for anyone), it may also help you shed some unwanted pounds without even thinking about it.

The study was published in the August 2010 issue of the American Journal of Preventive Medicine.