When elderly drivers have to stop getting behind the wheel, they run the risk of social isolation, especially if they don't have an alternative transportation plan, a recent study suggests.

The study looked at driving habits and social activities, like visiting friends and family or going out to dinner or the movies, for more than 4,300 adults over age 65.

With wheels, older adults were much more likely to be out and about than their peers who never drove, the study found. But after elderly drivers lost the ability to hit the road, their participation in social activities declined to match their peers who never drove at all.

"Social participation in old age is linked with both physical and mental health benefits," said study author Teja Pristavec, a sociology researcher at Rutgers University in New Brunswick, New Jersey.

"Older adults who remain engaged in social life report being in better health, experience lower mortality risk over time, and have lower rates of depression, dementia, and other cognitive impairments," Pristavec added by email. "Transportation mobility is often crucial for such continued social participation."

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Pristavec looked at survey data collected in 2011 and 2013 from people enrolled in Medicare, the U.S. health insurance program for the elderly.

Compared with seniors who had stopped driving, frequent drivers were more than three times as likely to visit friends and family and almost three times as likely to participate in social outings like going to the movies, Pristavec reported in the Journal of Gerontology: Social Science.

Frequent drivers were also more than twice as likely to attend religious services or organized group activities, the study found.

The analysis didn't include data on at whether seniors lived in rural or urban communities or whether they had easy access to public transportation, however, or how close they lived to friends or relatives who might be able to give them rides.

At least some people in the study may have stopped driving because they were depressed and uninterested in driving, or were physically unable to drive, noted Raymond Bingham, a researcher at the University of Michigan Transportation Research Institute in Ann Arbor who wasn't involved in the study.

Because the study didn't account for physical or mental health impairments, it's hard to say whether these problems caused seniors to stop driving or if the reverse is true - that losing access to transportation led to these problems, Bingham said by email.

In some instances, families and physicians will get clear signs it's time for a driver to stop getting behind the wheel - such as when older drivers make several right turns to avoid left turns at intersections or when they insist on having a passenger to help navigate so they can concentrate on traffic, Bingham noted.

But there's also a broad gray area where seniors may not be the best drivers on the road but they're not doing anything that's an obvious safety hazard.

"In that gray margin it would be important to consider how far the elderly patients have to drive to get to their destinations, how often do they need to drive, and whether or not there are safer alternatives available to them," Bingham added by email.

"I think it would be a difficult balance," Bingham said. "My parents decided for themselves that they were ready to quit driving, so I never had to intervene, for which I was grateful."