IIHS study contradicts government on roof crush—more lives could be saved

The Insurance Institute for Highway Safety (IIHS) has recently published a report looking at vehicle roof strength and its relation to protecting people in rollover crashes. This study raises serious questions about earlier U.S. Government studies that predicted a very minimal positive effect from strengthening vehicle roofs to prevent their caving in during rollover crashes. Before this study there was “no conclusive evidence about the specific contribution of a vehicle’s roof strength to occupant protection.” The IIHS report focused only on midsized, four-door SUVs, and it supports CR’s position on the importance of stronger roofs as one way to mitigate rollover injuries and deaths.

Background: The Government’s roof-crush standard, known as FMVSS 216, hasn’t changed in decades. It was implemented back in 1973 for cars, and extended to light trucks and vans in 1994. This standard specifies a test where a steel plate is pressed against the roof’s edge above the driver’s door and loaded up with a force equal to 1.5 times the weight of the vehicle. The roof is allowed to collapse no more than five inches. The federal government’s auto-safety agency, the National Highway Traffic Safety Administration (NHTSA), proposed in 2005 a revised test that would increase the load on the steel plate to 2.5 times the vehicle’s weight.

The upgraded standard also specifies that roof crush cannot exceed the space available above the head of a 50th-percentile male crash dummy. In a follow-up proposal dated January 2008, NHTSA suggested it might extend the test to include both the passenger and driver’s side of the vehicle, instead of just one side of the roof.

Benefits questioned: NHTSA has estimated that its new roof-crush standard would prevent only 13 to 44 fatalities per year. That’s out of some 10,000 rollover fatalities that occur annually. If the standard were raised to three times the vehicle weight instead of 2.5 times, NHTSA estimates life-saving at 49 to 135 fatalities. Meanwhile, NHTSA has pegged the cost to the industry for its new regulation at $88 to $95 million for the 2.5-times-weight load, but at more than 10 times that, $1.2 to $1.3 billion, for the 3-times-weight load.

The IIHS concludes that NHTSA’s life-saving estimates are far too conservative. The IIHS examined just 11 vehicles, midsized four-door SUVs. But it concluded that if they had all had roofs as strong as the strongest among them, the 2000-2004 Nissan Xterra, then about 212 of the 668 deaths that occurred in those SUVs in 2006 would have been prevented.

Both NHTSA and the IIHS assert in their reports that electronic stability control will go a long way toward preventing rollover injuries and fatalities because ESC seems to be highly effective at preventing rollover in the first place. However, even with ESC, vehicles can still trip over a curb and roll, or roll down an embankment. Higher roof strength limits would help prevent injuries form these accident scenarios. Side-curtain air bags are expected to reduce fatalities and injuries when a rollover does happen, both by cushioning occupants and by preventing occupant ejection.

Nevertheless, the IIHS believes that the link between roof strength and injury risk remains. For instance, even if a vehicle is equipped with side-curtain air bags, they may not work so well if the roof collapses and the vehicle’s doors pop open. “There will still be rollovers,” says the IIHS Communications Director Russ Rader, “even when all vehicles have stability control.”

—Gordon Hard

Read “Raising the roof standard for rollover safety.” See Consumers Union’s stand on roof crush from 2005. Learn more about car safety in our Safety section and in the CR Safety blog.