It's called the gray tsunami, the great wave of aging baby boomers nearing retirement, making older adults the fastest growing segment of the population. And by 2030, the roads will be full of them.

According to the Census Bureau, the number of people 65 and older is expected to double, growing from 35 million in 2000 to more than 71 million in 2030. The Insurance Institute for Highway Safety projected that by then, one in four drivers will be 65 or older, statistics that have safety experts studying how cars and the drivers themselves will need to adapt as the roads turn gray.

At the AgeLab at M.I.T. in Cambridge, Mass., for example, there are at least 20 aging studies looking at such factors as driver fatigue, the impact of technology inside the vehicle and how emotions and medications affect driving. States are also redesigning intersections to make them less confusing for older drivers. And organizations like AAA and AARP are advising older drivers about how to measure their abilities and are evaluating their cars to determine what adjustments need to be made to counter a driver's physical limitations.

Loren Staplin, a managing partner of TransAnalytics, a consulting firm specializing in transportation safety research and development, said that older people were usually superb drivers because of their lifetime of experience.

But as a consequence of aging, vision, mental and physical abilities often decline, he said, making it "more difficult for them to drive safely."

Many of these factors are being studied at the AgeLab. Miss Rosie, a Volkswagen New Beetle, is a mobile lab used for research into how flexibility and strength affect driving performance. Miss Daisy, another New Beetle and the AwareCar, a Volvo, are wired to track eye movements and to measure pulse, alertness and stress levels, as a measure of the kind of physical changes older people undergo while driving.

What many experts do agree would help older drivers is changing the design of roads, especially intersections, where drivers often have problems judging speed and distance. So some states are redesigning them. They are installing left turn lanes, left-turn signals, street signs well before the intersection and replacing eight-inch traffic lights with 12-inch ones.

The Road Improvement Demonstration Program, started by AAA Michigan and financed by state, county and local governments, made some of these changes at nearly 400 intersections. An analysis of the first 84 completed in the Detroit area showed the injury rate over a two-year period for older drivers was cut by more than half, compared with the rate for drivers 25- to 64-years-old. And the rate of left-turn collisions involving seniors dropped 73 percent when a left-turn signal was installed.