A 36-year-old roof strength standard has gotten a long-overdue upgrade that improves protection for people in rollover crashes and for the first time covers roofs on heavier pickup trucks and SUVs.
The new Federal Motor Vehicle Safety Standard 216 is tougher than the Institute expected. For lighter vehicles, the rule will require their roofs to be nearly as strong as needed to earn top ratings in the Institute's roof-strength rating program, which is designed to help consumers pick vehicles that will best protect them in rollovers. The rating system is based on Institute research showing occupants in rollovers benefit from stronger roofs (see "Roof strength affects injury risk in SUV rollover crashes, study finds," March 15, 2008, and Status Report special issue: roof strength, March 24, 2009).
"Regulators took a bold step with this rule," says Institute president Adrian Lund. "It's stronger than what was initially proposed in 2005 and will further encourage automakers to make roofs that also earn good ratings from the Institute."
Manufacturers have built cars to meet the same federal roof standard since 1973. The rule was extended in 1994 to include all passenger vehicles up to a gross weight rating of 6,000 pounds. Many SUVs and pickups were heavier, so they were exempt.
The National Highway Traffic Safety Administration (NHTSA) unveiled the rule in April after numerous delays. It doubles the current roof strength requirement for vehicles with weight ratings up to 6,000 pounds and requires roofs on vehicles with ratings of 6,000-10,000 pounds to withstand a force equal to 1.5 times their unloaded weight. Another requirement is that roofs maintain sufficient headroom during testing. Phase-in begins in September 2012, and all vehicles must comply in the 2017 model year.
For vehicles up to 6,000 pounds, both the driver and passenger sides of the roof must withstand a force equal to 3 times the vehicle weight before contacting a headform representing the seated position of an average-size man or before reaching 5 inches of crush, whichever comes first. This is called a strength-to-weight ratio. For the first time, the government also will require the same performance on both sides of the roof when tested sequentially.
The double-sided test is a departure from the current procedure in which a metal plate is pushed against only 1 side or the other of a roof at a constant speed. Now manufacturers will have to test 1 side and then the other. Both sides must demonstrate the required strength-to-weight ratio.
More than 10,000 people a year are killed in rollovers. When vehicles roll, roofs hit the ground, deform, and crush. Stronger roofs crush less, reducing the risk that people will be injured by contact with the roof itself and preventing people, especially those who aren't belted, from being ejected. Intact roofs help keep doors and windows in place.
NHTSA says 135 lives will be saved each year out of 667 fatalities it attributes to roof strength. It considers 93 percent of rollover fatalities to be unrelated to roof strength.
"We're glad to see the requirement for stronger roofs, but NHTSA still underestimates the benefits," Lund says. "We think many more lives will be saved. Strong roofs help maintain occupant survival space and also keep unbelted people inside vehicles as they roll. NHTSA doesn't think unbelted occupants or those at risk of ejection benefit from stronger roofs, but our research says they do."
An Institute study of 11 midsize SUVs found that a 1-unit increase in peak strength-to-weight ratio reduces risk. For example, increasing the ratio from 2 times vehicle weight to 3, measured on 1 side of the roof, reduces drivers' risk of serious injury or death in single-vehicle rollover crashes by 24 percent. An Institute study of 12 small 4-door cars yields similar results. Researchers estimated that a 1-unit increase in the peak ratio is associated with a 22 percent reduction in drivers' risk of serious or fatal injury in small cars (see "Roof strength affects injury risk in SUV rollover crashes, study finds," March 15, 2008, and Status Report special issue: roof strength, March 24, 2009).
"Applying these estimates to the number of deaths in single-vehicle rollovers of these vehicles in 2007 indicates that 189 of 931 driver and right-front passenger deaths would have been prevented," Lund says. "These are the lives saved if the roofs on just those 23 SUVs and cars we studied had strength-to-weight ratios of at least 3 times the vehicles' weight. That's only 2 small groups of vehicles. The government's 2-sided test means roofs will be even sturdier. We look forward to seeing many more lives saved as roofs get stronger."
Independent of NHTSA's rulemaking action, the Institute in March launched a roof strength rating system to drive improved rollover crash protection the same way the Institute's frontal offset and side consumer test programs have led to better protection in these kinds of crashes. To earn a good rating, a roof must withstand a force of 4 times vehicle weight before reaching 5 inches of crush in a 1-sided test. For acceptable, the minimum required strength-to-weight ratio is 3.25. A marginal value is 2.5. Anything lower than that is poor.
Institute research shows a ratio of 4 reflects an estimated 50 percent reduction in the risk of serious and fatal injury in single-vehicle rollovers compared with a 1.5 ratio.
"We plan to continue rating vehicle roof strength for the foreseeable future," Lund says. "The leisurely phase-in of the new standard means roofs won't have to get stronger right away. We want to reward those manufacturers who are ahead of their competition when it comes to providing rollover crash protection and also help consumers identify the safest vehicle choices."
Small SUVs were the first vehicles tested under the program. Results for minicars will be released this summer.