Alarmed by his increasingly risky behavior behind the wheel, the result of end-stage congestive heart failure and accompanying dementia, and stymied by his refusal to take taxis or the private minibus that provided door-to-door service around his Boston suburb, my sister and I decided we had to act. She held onto the car keys that he had given her for safekeeping during a brief hospitalization and, without telling him, called his doctor, who broached the subject during one of my father’s increasingly frequent appointments. Then we both refused to give him back his keys unless he passed the two-part test that I scheduled for him.

We were surprised when he aced the first part, which assessed cognitive function and mobility. By the time the driving exam rolled around several weeks later, in November 2006, the matter was moot. He had fallen and was in a nursing home where he died peacefully a few weeks later, never having learned that his children had dropped a dime about his driving.

My family’s dilemma — whether and how to intervene when a potentially dangerous elderly driver, often a parent, refuses to hang up the keys — “is happening all across the United States in families up and down the streets every day,” said Elinor Ginzler, a senior vice president of AARP. “It’s a huge issue.”

Impairment, not age

Ginzler and other geriatrics experts predict that the issue will explode in the next decade as the leading edge of the 78 million-member baby boom generation hits its 70s. In 2008, according to the Insurance Institute for Highway Safety, 78 percent of the 28 million Americans older than 70 had licenses, up from 73 percent in 1997, an upward trend that is expected to continue.

Because more Americans are living longer with progressive, disabling diseases that make driving iffy or downright dangerous — heart problems, stroke, Parkinson’s, dementia and diabetes, to name a few — families are increasingly wrestling with questions that defy easy answers. Although many seniors stop driving voluntarily or sharply limit their driving, others refuse. Some fear being marooned in their suburban homes, while others, like my father, cling tenaciously to the independence a car represents, unaware of how hazardous their driving has become. A survey by the MIT AgeLab and the Hartford insurance company found that age enhances confidence in driving ability. Drivers 75 and older were twice as likely to say they planned to drive into their 90s as did those 65 to 74.

Such confidence can belie reality. A 2007 report by the Government Accountability Office found that drivers 75 and older were more likely than drivers in all other age groups, including adolescents, to be involved in a fatal crash.

“In the old days, or even 20 years ago, people just did not live long enough for this to be a problem,” said Elin Schold-Davis, head of the American Occupational Therapy Association’s Older Driver Initiative, who notes that some older drivers are taking potent medications that fog concentration. “People are living with a level of impairment that is unprecedented. And these days driving is more complicated. There’s more congestion, more complicated signs and traffic patterns,” while cars no longer demand the physical strength required before power steering and power brakes.

Drivers with dementia are of particular concern. One study estimated that 4 percent of drivers older than 75 have dementia, and many drive until the disease is advanced. In April the American Academy of Neurology issued new guidelines stating that some people with mild dementia may be able to continue to drive. The recommendation is based on research that found that 76 percent could pass a road test.

Spurred by highly publicized fatalities caused by elderly drivers, a growing number of states are tightening restrictions, requiring vision exams, in-person license renewals or a doctor’s approval to retain a license. But according to the National Highway Traffic Safety Administration, there is no single test or screening tool that will reliably weed out unsafe older drivers.

Often it falls to family members, who are most familiar with the driver’s condition, to take action. But the emotions such decisions unleash can be anguishing, igniting conflict among siblings and creating resentment in parents who feel their meddlesome children are bossing them around or, worse yet, ratting them out. Because such discussions invariably occur at a time when loss — of a spouse, close friends, health, independence — dominates, giving up driving can be a terrible blow, particularly for men.

“Driving is an issue of control,” Ginzler said. “It’s a mistake to say, ‘This isn’t a big deal.’ It’s a very big deal.”