This week's tragedy in Santa Monica, Calif., in which an out-of-control car killed 10 people and injured dozens at a farmers' market, has revived a question that will become increasingly urgent in coming years: Should states place restrictions on older drivers, or even take away their licenses?

On Wednesday, Russell Weller, 86, drove his sedan along the open-air market, knocking down stalls and hitting as many as 50 people.

The incident brought to mind similar fatalities from this area. In March, for example, a 92-year-old woman ran over and killed a fellow resident in a Lebanon retirement community. Experts say the failing eyesight, slowing reaction time and reduced attention span that often come with advanced age contribute to crashes. Often, there are warning signs; Weller had hit his own garage twice recently. Are states doing enough to check for such signs?

According to the Insurance Institute for Highway Safety, 21 states have requirements for older drivers, but most merely make them renew licenses every three years instead of four - as Indiana does - or in person instead of by mail. Only a handful require vision tests; only New Hampshire and Illinois require a road test.

Ohio and Kentucky have no special requirements; Ohio retests an older driver only if a doctor, relative or police officer requests it or if the driver has been in a crash where age was ruled a contributing factor. In 1998, Indiana actually stopped testing drivers aged 75 and older.

It may be unfair to set an arbitrary driving age limit. Thanks to medical advances, Americans are living longer, but also enjoy improved health and vitality in old age. The Insurance Institute says older drivers are as safe as younger ones until age 75, when the accident rate increases.

AARP, the powerful seniors' lobby that opposes driving bans, advocates better testing. But proposed annual driving tests or extra training nationwide would be very expensive.

There are alternatives. Two years ago, a UCLA psychiatry professor developed a quick, inexpensive test to pinpoint a loss of cognitive ability that's directly related to increased accident risk in older drivers. States should explore options and make policy changes soon. By 2030, about 25 percent of all U.S. drivers will be over the age of 65.

Those drivers should retain the right to drive as long as they can drive safely. But states need to do more to determine just who - regardless of age - can drive safely.