Lewis Morgenstern has made up his mind. When he turns 65 in four years, he’s going to sign an advance directive for driving.

The directive will say that when his children want him to stop getting behind the wheel, Morgenstern will follow their advice.

“I recognize that I might not be able to make the best decision about driving at a certain point, and I want to make it clear I trust my children to take over that responsibility,” said Morgenstern, a professor of neurology, neurosurgery, and emergency medicine at the University of Michigan.

Relatively few studies have looked at how many older adults with mild cognitive impairment or dementia continue to drive, and there aren’t any national standards on when people should hand over the car keys. But the issue is a growing concern as the ranks of seniors in their 70s, 80s, and 90s — the age group most likely to have cognitive impairment — expand.

Nearly 50 million people 65 and older held driver’s licenses in 2021, a 38% increase from 2012, according to data compiled by the American Automobile Association. Almost 19 million were 75 or older, a rise of 31%. During this period, motor vehicle deaths for people 65 and older increased 34%, reaching 7,489 in 2021. The number of seniors injured in vehicle crashes that year exceeded 266,000.

For the most part, older adults drive safely. They use seat belts more often, are intoxicated less often, and are less likely to speed than younger adults. Compared with younger and middle-aged adults, they’re involved in fewer fatal car crashes each year. And they’re more likely to restrict where and when they drive — following familiar routes, avoiding heavily trafficked streets, and not driving at night.

Still, risks for older drivers rise with advancing age and the onset of medical conditions such as arthritis, glaucoma, and Parkinson’s disease. And when crashes occur, seniors are more likely to be severely injured or die because they’re more vulnerable physically.