"Older drivers who do continue to drive are relatively safe," said David Loughran, lead author of the study and a senior economist with the RAND Corporation. "It's unclear if the benefits of improving licensing regulations based solely on age outweigh the costs. At best, the evidence on safety is ambiguous."

"This report looked at a larger number of crashes, so we finally have definitive evidence that older drivers are safer. We always say 'older drivers are wiser drivers,' " said T. Bella Dinh-Zarr, director for North America of Make Roads Safe, a nonprofit organization. "This will have significant policy implications, because it gives evidence that older drivers don't pose a risk to others as much as they pose a risk to themselves. We can look at ways to improve safety for older drivers rather than just regulations and being so draconian about some of policies."

Senior driving has long been a concern of policymakers. Many states, assuming that older drivers are more dangerous, have imposed stricter licensing requirements on seniors. Additional requirements are being considered as the population ages.

The concern has been fueled by a few high-profile incidents. In July of 2003, an 86-year-old man drove his car into a crowd of shoppers at a Santa Monica, Calif., farmers' market, killing 10 and injuring more than 50.

In October of 2005, a 93-year-old man struck a pedestrian in St. Petersburg, Fla., and only noticed the corpse hanging out of his windshield when alerted by a tollbooth operator.

According to the report, by 2025, drivers aged 65 and older will comprise one-quarter of the driving population.

Medical evidence is clear that, as people age, their ability to drive safely does become compromised. Loss of vision, including macular degeneration, glaucoma and cataracts, is a leading contributor to this problem.

On the other hand, many older drivers compensate for these changes by altering their driving behavior, experts say.

"Older drivers tend to self-regulate," Dinh-Zarr said. "They don't drive at night. They're careful about highway driving and intersections where they're more likely to be in a crash. They're already doing fairly good job on their own because they know their bodies have changed."

So, just how risky are older drivers?

The RAND study found that people 65 and over accounted for 15 percent of all licensed drivers but only 7 percent of all accidents in the United States.

Younger drivers (aged 15 to 24) accounted for 13 percent of all licensed drivers yet caused 43 percent of all accidents.

But because of fragile health, older drivers are seven times more likely than their younger counterparts to be killed in a two-car accident.

Older drivers also tend to drive less than younger drivers, racking up 38 percent fewer miles than adult drivers, while teens and younger adults drive about 54 percent more miles than adult drivers. This indicates that many may be self-regulating.

Implementing different and better safety measures may make more sense than more stringent licensing for older people, the study stated.

Others agreed.

"It's not just a transportation issue, it's a public health and quality of life issue," Dinh-Zarr said. "We need to work on interventions that are good for seniors, which thankfully will also be good for the rest of us, such as better lighting, safer intersections and better energy absorbent materials in interiors of vehicles."

More information

Visit the RAND Corporation for more on the report.