Fasten your seat belt. The Bush administration's proposal to require that vehicle roofs be made stronger -- in hopes of reducing deaths and injuries from rollover accidents -- promises to be as bumpy a regulatory ride as the implementation of air bags in cars and trucks. The air-bag rule took years to put in place and inflamed the acrimony that exists between safety groups and the auto industry.

On Nov. 21, the comment period closed for the National Highway Traffic Safety Administration's so-called "roof-crush rule," a modification of a 30-year-old standard that long has been criticized as weak and ineffective. Rollover accidents are responsible for 24,000 injuries and 10,000 fatalities annually -- one-third of all people killed in auto crashes.

NHTSA said 807 people wearing seat belts are seriously injured and an additional 596 die annually in rollovers that involve occupants making contact with the roof, or "roof intrusion." Two-thirds of those killed in all rollovers weren't wearing seat belts at the time of the crash, according to agency spokesman Rae Tyson.

Despite the sobering statistics, the proposal calls for only a modest increase in roof strength, inclusion of large sport-utility vehicles and vans, and protection for car manufacturers from lawsuits brought by victims of rollovers in which the roof is involved.

It says that vehicles up to 10,000 pounds would have to withstand force applied to the roof that are 2.5 times vehicles' unloaded weight and that the roof cannot touch an occupant's head. The current rule, which predated the flood into the market of sport-utility vehicles that are more prone to roll over, requires vehicles to withstand force of 1.5 times the vehicle's weight on the roof, up to 5,000 pounds.

Notably, two-thirds of car and light truck models on the road already meet the proposed standard. The agency estimated that the average cost of strengthening the roof for vehicles that don't meet the new standard would be $58.6 million annually, or $10.67 per vehicle. Automakers will have three years to implement the rule after it becomes final.

NHTSA estimates that the improvement in roof strength will save only 13 to 44 lives and prevent 498 to 793 injuries. That's because some rollover accidents are so violent that no amount of roof strengthening would save the occupants, the agency said, without other improvements, such as side air bags. Public Citizen, a consumer group that advocates safer vehicles, disagrees and said a strong roof-crush rule would save thousands of lives.

Thus, highway safety groups have lambasted the proposal. "It's virtually a nothing burger," said Joan Claybrook, president of Public Citizen. "This proposal is useless."

Updating the rule has been at the top of the wish list for safety groups for many years. At the same time, the number of court cases blaming weak roofs for injuries and fatalities has increased.

Carmakers, meanwhile, say no rule is going to prevent serious injury when a vehicle tips over, especially if the occupants are not wearing seat belts. Over the years, companies such as Ford Motor Co. and General Motors Corp. have insisted that injuries occur before the roof caves in.

"Both Ford and Volvo have looked at injury and fatality rates in rollovers involving vehicles that meet the federal standard to vehicles that have roof strengths that are multiples of the federal standard, and there isn't a difference," said Kathleen Vokes, a Ford spokeswoman, in a statement. Volvo is a Ford subsidiary.

The animosity between the auto industry and safety groups is apparent in the fate of the "Volvo documents" that advocates of a tougher rule tried to include in comments to the agency.

The documents show how Volvo made its XC90 model roofs stronger than the norm by designing a "steel cage" to protect occupants in rollovers. They came up in a trial in Jacksonville, Fla., last spring in which a jury awarded $10.2 million to the family of Claire Duncan, a 26-year-old engineer. The jury found the roof in a Ford Explorer to be defective. Ford is appealing.

The papers include e-mail traffic between the two companies in which Ford tells its subsidiary that it must cease its emphasis on roof strength and get in step with Ford's position on the issue.

The documents were then placed in the NHTSA rulemaking docket. But the agency removed them after Volvo said they were under a protective court order.

Last Thursday, Public Citizen petitioned the Florida state court to make the papers public, claiming they are directly relevant to the current rulemaking. Ford, in a statement, said the documents should be kept from the public because they contain trade secrets.

This twist in the process isn't likely to change much about the final rule, especially since the auto industry says it can meet it easily.

In fact, safety groups also complain that the test for meeting the standard is too weak. NHTSA's proposal includes a test that uses a steel plate or "arm" to crush the roof on one side of the vehicle. The amount of intrusion into passenger space is then calculated. Safety advocates want a test that would replicate the multiple flips that happen in a rollover, which the agency rejected.

Manufacturers stress that other NHTSA rulemakings would better enhance occupant safety, such as side air bags to keep passengers from being ejected from vehicles and requiring stability control systems to keep the vehicle on the road.

"The thing that is getting lost in the weeds is you have to look at all the various initiatives the agency has," said Robert Strassburger, vice president for safety and harmonization for the Alliance for Automobile Manufacturers. "The roof-crush rule will be more of a backstop than anything else."