WASHINGTON -- The Insurance Institute for Highway Safety said Wednesday it will require automakers to dramatically increase the strength of vehicle roofs to receive its top safety pick ratings.

The Virginia-based IIHS conducts dozens of crash tests annually and prods automakers into adding safety features to reduce car crashes injuries and deaths. Its ratings are widely used by consumers and touted by companies that win them. Automakers often make design changes to boost their ratings.

Adrian Lund, president of IIHS, said Wednesday another study it commissioned had convinced the Institute that it was time to require automakers to do more to improve roof strength. A study being released today by IIHS, which is an industry funded group, at the SAE Government/Industry meetings shows that a 1.0 increase in roof strength reduces the risk of fatalities in a single-passenger car rollover by just over 20 percent, Lund said.

In January, the National Highway Traffic Safety Administration unveiled a proposal to require a vehicle roof to withstand a force equal to 2.5 times the vehicle weight while at the same time maintaining sufficient head room for a buckled-in, average-size adult male to avoid being struck. That's up from the current standard of withstanding a force equal to 1.5 times the vehicle weight. But NHTSA hasn't finalized its regulation.

Lund said starting in the fall IIHS will require automakers to have a 4.0 rating to win a top safety pick.

"We see significant safety benefits in stronger vehicle roofs," Lund said.

"The government is moving slowly and they are going to continue to move slowly."

He said NHTSA has "clearly undercounted" the number of injuries and deaths that can be prevented by stronger roofs.

The Alliance of Automobile Manufacturers, the trade group that represents Detroit's Big Three automakers, Toyota Motor Corp., Daimler AG and six others, supports increasing the standard to 2.5 times the vehicle's weight, but says going beyond that is unwarranted.

In December, the Bush Administration abandoned efforts to comply with a congressional deadline to update the standard. It was the third delay in finalizing the standards and Transportation Secretary Mary Peters said the new rule would be in place by April 30.

Ron Medford, a senior associate NHTSA administrator, said Wednesday at the SAE meetings in Washington that the administration had "punted for the third time" and had set the new date "without consulting with us quite frankly."

Medford said it wasn't clear if they could meet the April 30 deadline.

"The important thing is to do it right," he said.

"This has been a very controversial rule. It's been hard in terms of policy decisions," Medford added. "There's just a lot of attention on this."

He said the alliance was interested in learning more about IIHS's new rating system. NHTSA's proposed update also would cover vehicles that weigh up to 10,000 pounds, versus the current 6,000-pound requirement.

The proposal is aimed at helping people survive rollover crashes, which account for more than 10,000 deaths annually. Rollovers represent 3 percent of all crashes, but account for one-third of all vehicle deaths.

General Motors Corp. and Ford Motor Co. essentially wrote the regulation that's been in effect since 1973 after their fleets failed NHTSA's first proposed roof standard in 1971.

NHTSA studied the issue for more than a decade before proposing in August 2005 to increase the strength of vehicle roofs and broaden the number of the vehicles covered.

NHTSA said then that upping the standard to 2.5 times the vehicle weight would save 13 to 44 lives and prevent up to 800 injuries annually. The agency said it would require that both sides of the vehicle roof be tested, and in January, NHTSA updated its proposal to include a double-sided test. Currently, only one side is tested.

The Auto Alliance also noted that increasing roof strength requires making roofs heavier -- reducing fuel efficiency -- and raising costs. It supports increasing the standard to 2.5 times, but with significant modifications to the proposed rules, including a phase-in schedule.

"Drivers and passengers are better served by a system of enhancements including improvements in vehicle stability, ejection mitigation, roof crush resistance as well as road improvement and behavioral strategies aimed at consumer education," alliance spokesman Wade Newton said.

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