Currently, just over one in six licensed drivers in the United States are 65 and older. But that figure is tipped to reach one in five by 2025, according to the study by TRIP, a transportation industry-sponsored research group that works to improve highway conditions.

Although drivers 65 and older presently account for 8 percent of all highway miles driven, they comprise 17 percent of all traffic fatalities, according to the study.

"There is a significant concern about a growing number of older motorists navigating difficult traffic situations," Frank Moretti, director of policy and research for TRIP, said on Thursday.

The group's report, which calls on states to make roads safer for seniors, was done in conjunction with the American Association of State Highway and Transportation Officials.

The number of traffic fatalities in the United States in 2010 was the lowest in 60 years, despite the nation's growing population, the report said. But TRIP says that as the population ages, those numbers may start going back up.

In three states - Connecticut, West Virginia, and Florida - one in five licensed drivers is over 65, and the share of the total drivers who are elderly is going up in nearly every state, Moretti said.

Helpful changes would include better street lighting as well as "clear and brighter signage, with better and bolder lettering."

He said traffic engineers should think about lengthening merging lanes and exit lanes for major highways, and adding rumble strips to notify motorists that they are approaching intersections. And he said older drivers and their families would benefit from education that would help them identify at which point they should stop driving.

"The growing ranks of older Americans will far outpace previous generations with their level of mobility and activity," TRIP executive director Will Wilkins said. "Serving their needs will require a transportation system that includes safer roads, safer vehicles, safer drivers, and improved choices."

The group said older motorists shun public transportation, with more than 90 percent choosing to drive their own vehicles. In many cases, seniors resist giving up driving, even when they realize that their eyesight and other senses are not up to the task, because they see driving as proof that they remain active and worthwhile.

TRIP's recommendations include better evaluation of older drivers and tightening license requirements to ensure older motorists are tested regularly.

(Reporting By Jim Forsyth; Editing by Corrie MacLaggan and Eric Beech)

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