WASHINGTON - Few car seats and head restraints offer adequate protection for passengers in rear-end crashes, according to a new insurance industry study that could pressure automakers to improve seat and headrest design.

The Insurance Institute for Highway Safety, an independent research group funded by insurance companies, said only eight of 73 seats it subjected to a new crash test provided good protection against neck injuries such as whiplash. Another 16 were deemed "acceptable."

Another 24 seats failed a more basic test by not providing head restraints high enough to reach the heads of tall passengers.

For the first time, the group used crash dummies to measure the effectiveness of car seats to prevent injuries in a rear-impact crash at low to moderate speeds.

"It's obvious that some automakers are doing a better job than others of designing seats and head restraints to protect their customers' necks in rear crashes," said Adrian Lund, chief operating officer of the insurance institute.

The new study will join influential insurance institute ratings for passenger protection in frontal and side crashes. The institute publishes the ratings on its Web site, www.iihs.org, and through a newsletter. The ratings are widely used in shopping guides targeted at consumers in the market for a new car or truck.

In response to poor scores in previous safety studies by the insurance industry, automakers have rushed to improve car and truck designs in response to poor scores, but they reacted cautiously to the new rankings.

Eron Shosteck, a spokesman for the Alliance of Automobile Manufacturers in Washington, said automakers will study the test results and evaluate whether they provide useful information to consumers.

"Automakers are committed to safety," Shosteck said. "They are always evaluating new information that can help with future design changes that can improve safety."

While neck injuries caused by poor seat designs are not generally life-threatening, they are painful. Symptoms including headache, dizziness, and tingling in the arms that can last from a few hours to several years.

Whiplash injuries are common in rear-end crashes. The insurance industry estimates there are more than 250,000 neck injury cases a year. Treating the injuries costs the insurance industry $7 billion a year.

General Motors Corp., in a statement, said it has led in seating system designs with innovations such as its self-aligning head restraint, a device that moves the head restraint up and forward dynamically during a rear crash.

"While the study of whiplash is not fully understood, GM has been a leader in moving head restraints higher and more forward in conjunction with the (insurance institute) guidance on neck protection," GM said. "People come in all shapes and sizes and are seated in various positions in a vehicle. If the test methods chosen are not reflective of reducing real-world harm, there could be significant potential to cause seat design changes that are directionally wrong."

In the new tests, the institute identified positioning and seat stiffness as two keys to protecting a passenger in a rear-impact crash.

The seating system must ensure the passenger will contact the head restraint at the right angle. The restraint has to be high enough and close enough that the head doesn't snap back - the classic cause of whiplash injuries.

Similarly, the seat itself has to be stiff enough so the back does not collapse, but not so stiff that it injures a person.

The best seats act like catchers' mitts, absorbing the blow of the body flying back during the crash.

Of the cars tested, Volvo and Saab models received the highest marks from the insurance institute, with five of their models rated as "good." Jaguar's S-Type sedan and the Subaru Impreza also achieved the highest rating.

The Volkswagen New Beetle equipped with active head restraints and lumbar support also was rated good, while models with other types of seats were rated acceptable.

At the other end of the scale were 24 models that could not pass the group's basic test. The models had head restraints that were too low or too far away to prevent neck injury. The institute did not subject the cars to the new, more rigorous test but automatically rated them "poor."

GM was the worst offender on "bad geometry," the institute noted, with two-thirds of the failing models.

Susan Ferguson, senior vice president for research at the insurance institute, said adjustable head restraints pose another problem. Many consumers aren't aware of how important the head restraints can be in a crash and do not bother to adjust the restraints. There is a common misperception that the restraints are really just "headrests."

"If they are adjustable, and they are not adjusted up, they won't do you any good," Ferguson said.

The institute recommends an adjustable restraint be positioned at least level with the top of the ears, about 3.5 inches below the top of the head. For the restraint to work properly, the distance between the back of the head and the restraint should be as small as possible, and no more than 4 inches.

The federal law that dictates a minimum performance level for head restraints has not been updated since 1969. A proposal to toughen the requirements has been pending since 2001.

In the meantime, automakers have been improving seats and head restraints on their own.

When the insurance institute began to measure head restraints for height and distance to the back of the head in 1995, only 3 percent were rated good and 82 percent poor. By 2003, 45 percent got the good rating, and the number deemed poor had dropped to 10 percent.

The new, tougher insurance institute test is designed to simulate what would happen if a car was struck from behind by another vehicle going 20 mph. Institute engineers first remove the seats from a vehicle and mount them on a sled. For the first time, crash-test dummies designed specifically for rear-impact tests were used.

The sled, mounted on fixed rails, is moved with forces similar to a real-world crash, with a maximum acceleration of 10 G's, or 10 times the force of gravity. The test lasts 91 milliseconds.

The insurance industry effort was part of a worldwide campaign to promote better seat designs. The insurance institute worked with its counterparts in Canada, Australia and Europe to design the seat test. Automakers also are receiving seating system rankings in other countries today.

You can reach Jeff Plungis at (202) 906-8204 or jplungis@detnews.com. Source: Insurance Institute for Highway Safety Source: Insurance Institute for Highway Safety