Lauran Neergaard

WASHINGTON: Families may have to watch for dings in the car and plead with an older driver to give up the keys — but there’s new evidence that doctors could have more of an influence on one of the most wrenching decisions facing a rapidly aging population.

A large study from Canada found that when doctors warn patients, and tell driving authorities, that the older folks may be medically unfit to be on the road, there’s a drop in serious crash injuries among those drivers.

The study, in today’s New England Journal of Medicine, couldn’t tell whether the improvement came because those patients drove less, or drove more carefully once the doctors pointed out the risk.

But as the number of older drivers surges, it raises the question of how families and doctors could be working together to determine whether and when age-related health problems — from arthritis to frailty to Alzheimer’s disease — are bad enough to impair driving.

Often, families are making that tough choice between safety and independence on their own.

“It’s very scary,” said Pat Sneller of Flower Mound, Texas, who talked her husband, Lee, into quitting about a year after he was diagnosed with early-stage Alzheimer’s disease.

The couple had recently moved from California, one of the few U.S. states that require doctors to report drivers with worrisome health conditions to licensing authorities.

Pat Sneller was stunned to learn Texas doesn’t require that doctor involvement, and health workers advised her to ride with her husband and judge his abilities for herself.

Eventually her husband called home in a panic, lost while driving in unfamiliar Dallas for volunteer work. A long scrape on the car that he couldn’t explain was the final straw.

In 2010, she persuaded him to quit driving, although the now-72-year-old’s license remains good until 2014.

“He still says occasionally, ‘I can still drive, you know,’?” Pat Sneller said.

By one U.S. estimate, about 600,000 older drivers a year quit because of health conditions. The problem: There are no clear-cut guidelines to tell who really needs to — and given the lack of transportation options in much of the country, quitting too soon can be detrimental for someone who might have functioned well for several more years.

It’s never an easy discussion.

Unlike in most of the United States, doctors in much of Canada are supposed to report to licensing authorities patients with certain health conditions that may impair driving. Ontario in 2006 began paying doctors a small fee to further encourage that step.