HOLLYWOOD’S action heroes may thrill audiences with well-timed leaps from crash-bound cars, but trying such a stunt in the real world is bound to be painful. In fact, federal statistics make it clear that exiting a vehicle in the course of an accident almost always leads to serious injury — and is often fatal.
A safety standard issued by the National Highway Traffic Safety Administration on Jan. 13 is intended to prevent occupants from being ejected through the side windows in accidents. The final rule requires automakers to incorporate technology designed to protect both belted and unbelted passengers.
In a news release, N.H.T.S.A. said the newly mandated system “prevents the equivalent of an unbelted adult from moving more than four inches past the side window opening in the event of a crash.” According to N.H.T.S.A. studies, more than half of those who died in ejection incidents were unbelted.
The agency says that in 2001-7 more than 10,000 deaths resulted from rollovers. According to its Fatality Analysis Reporting System, 47 percent of vehicle occupants killed in 2000-9 rollover accidents were fully ejected.
N.H.T.S.A. estimates that the safety technology will cost $31 per vehicle and predicts that it will save 373 lives and prevent 476 serious injuries annually.
The new rule will be phased in over several years. Large-volume automakers will have to install ejection-mitigation provisions in 25 percent of their vehicles starting in September 2013, with 100 percent compliance required by September 2017.
Smaller makers will not have to meet the phase-in schedule, but they must reach the 100 percent level in 2017. Convertibles and police vehicles are exempt, as are taxis and limousines with security partitions.
Along with the rule, N.H.T.S.A. developed test procedures to verify the effectiveness of the systems. The test requires that a linear impactor — a device shaped like a human head and attached to a shaft — be fired at the window area in several specific locations and at a designated speed.
To pass, the system must prevent the impactor from traveling more than a limited distance beyond the plane of the window — a stipulation that might necessitate tethers attached to the car to keep the air bags in place. The safety agency has also encouraged automakers to install stronger window glass.
It is worth noting that N.H.T.S.A. uses the term “ejection mitigation,” an acknowledgment that there is no practical way to provide total protection. In the vernacular of safety, there are few absolutes.
In contrast to earlier safety standards, the government is not leaving it up to automakers to determine which technology is used to meet the standard. Rather, it is requiring carmakers to develop side-curtain air bags that, when deployed, will cover the full opening of each side window adjacent to the first three rows of seats and a portion of any windows in a cargo area.
Steve Cassatta, a senior staff engineer at General Motors, said in a telephone interview that rollover-capable side-curtain air bags were part of G.M.’s strategy before the new rules went into effect. “From a technology standpoint, it isn’t inconsistent with our approach,” he said.
Current side-curtain air bags, engineered to be effective with seat belts, deploy from above the windows and help protect occupants in side impacts and rollovers. But they do not provide enough window coverage to assure that unbelted passengers will be kept inside the vehicle.
Jim Vondale, who until recently was the director for automotive safety for Ford Motor — the company that introduced side-curtain air bags in 2002 — said in a telephone interview that to meet the ejection test requirements, the curtain air bags would have to be considerably larger than those in today’s vehicles. He said the air bags would be tucked behind the headliner and roof pillar trim, possibly intruding on interior space somewhat.
Safety standards mandated by the government have generally been engineered with the presumption that safety belts were being used. Some experts see a risk that the new regulation, by mandating protection for unbelted occupants, could undo the decades of progress that have resulted from campaigns that promoted belt use.
“One of the concerns we have about having to design systems that protect unbelted people is it sends an inconsistent message,” Mr. Vondale said. “We want to consistently say that the most important element is the safety belt.”
In an e-mail, N.H.T.S.A. responded this way: “Even with the added protection resulting from the ejection mitigation standard, we know the best way for motorists to stay safe is to wear their seat belts — every trip, every time.”