Washington ? How old is too old to drive? States are taking a harder look as the number of elderly drivers increases.

Accidents like the one in Santa Monica, Calif., where an 86-year-old driver killed nine people and injured dozens more Wednesday when he drove into a crowded farmers market, are cited by those who believe older drivers should have to prove their capability.

But others point to statistics showing that older drivers are safer than teens — at least until they reach 75 — and are less likely than other drivers to drive drunk.

“It’s tricky. You can’t just as a matter of course say, ‘Once you reach 85, you can’t drive anymore,'” said Susan Ferguson, senior vice president of research at the Insurance Institute for Highway Safety, which is funded by auto insurers. “It would take driver’s licenses away from people who are perfectly fine to drive.”

In 2001, 16 percent of drivers were 65 and older; by 2030, one in four is expected to be in that age group.

At least 21 states, not including Kansas, have requirements for older drivers, varying from more frequent license renewals to vision tests. Two states — New Hampshire and Illinois — require road tests for those 75 and older, while in Nevada drivers 70 and older who renew licenses by mail must include a medical report.

A bill in the California Legislature requiring road tests for people 75 and older was killed in 2000 after senior citizen groups protested. Among those who would have been affected: Russell Weller, the man police say was responsible for the Santa Monica crash.

Weller told police he may have hit the gas pedal instead of the brake when he plowed through the farmers market. Weller was taken to a hospital for a blood test, and initial results found no traces of alcohol or psychoactive drugs such as antidepressants and hallucinogens.

AARP, the advocacy group for people 50 and older, favors better tests rather than age limits for drivers.

“We need to develop means to determine who can drive safely and who can’t,” said Cheryl Mattheis, AARP’s director of state affairs. “People should be able to drive as long as they can drive safely and effectively.”

Taking away a license can rob older people of their independence, forcing them to rely on others for trips to the grocery store or doctor’s office. AARP and the auto club AAA have programs to help such drivers keep their skills.

“We think whether someone continues to drive or not should be based on performance not just simply age,” AAA spokesman Mantill Williams said.

Some states give special benefits to older drivers. For example, Tennessee licenses issued to people 65 and older don’t expire and North Carolina doesn’t make people 60 and older parallel park during the road test.

Statistics from the Insurance Institute show that older drivers generally are as safe as other age groups until they reach 75, when they tend to have more accidents.

Drivers 85 and older are about as likely to be involved in a fatal crash as those ages 16 to 19, but they’re more likely to die than others in car accidents because their bodies are frailer, the institute’s Ferguson said.

Wendy Stav, an assistant professor of occupational therapy at Cleveland State University, said older people were more apt to have health issues that affect driving. For example, people with heart disease or diabetes can have conditions that cause them to lose feeling in their feet.

Other conditions that can affect older drivers’ performance are decreases in attention span, failing vision, inability to see well at night or in the rain, slowing of reaction time and decreased ability to do more than one thing at a time, Stav said.

Stav, who’s written a book on driver rehabilitation, said the best way to identify impaired older drivers was to have them evaluated by doctors or by driving evaluation programs through rehabilitation hospitals or state motor vehicle departments.

The American Medical Assn. plans to issue guidelines this month outlining things for doctors to look for that indicate someone’s driving skills are diminished.

The Insurance Institute is trying to find a state motor vehicle department willing to participate in a study that would use pamphlets that help older people and their families identify conditions that impair driving, Ferguson said.