The Institute has launched a new roof strength rating program to help consumers pick vehicles that will protect them in rollovers. Twelve small SUVs are first to the test, and only four earn the top rating of good. The Volkswagen Tiguan has the strongest-rated roof, and the Kia Sportage has the weakest among the 2008-09 small SUVs evaluated.
This new rating system is based on Institute research showing that occupants in rollover crashes benefit from stronger roofs (see "Roof strength affects injury risk in SUV rollover crashes, study finds," March 15, 2008). Vehicles rated good must have roofs that are more than twice as strong as minimum federal safety standards require.
The Tiguan, Subaru Forester, Honda Element, and Jeep Patriot earn good ratings. The Suzuki Grand Vitara, Chevrolet Equinox, Toyota RAV4, Nissan Rogue, and Mitsubishi Outlander are rated acceptable. Roofs on the Honda CR-V and Ford Escape are marginal, and the Kia's is poor.
"We anticipate that our roof strength test will drive improved rollover crash protection the same way that our frontal offset and side impact consumer test programs have led to better protection in these kinds of crashes," says Institute president Adrian Lund.
VW Tiguan: Good
The Tiguan has the strongest roof of the 12 rated SUVs. Its roof crushed less than 2 inches while withstanding a force of 15,000 pounds. That's 4 times the Tiguan's weight.
Kia Sportage: Poor
The Sportage has the weakest roof among the small SUVs the Institute rated. It crushed to 2 inches with half the force it took to crush the Tiguan's roof the same distance. The Sportage's roof crushed down past the driver's head restraint before the roof was able to withstand the same force as the Tiguan.
Institute research indicates that roofs have gotten stronger during the past few years. Part of the reason is that manufacturers have made structural improvements to earn better front and side ratings in Institute crash tests. Strong A and B pillars help prevent intrusion in these types of crashes and also help hold up the roof.
"It's not surprising that Volkswagen and Subaru earn good ratings in our new roof test because these automakers were among the first to ace our front and side tests," Lund points out.
More than 10,000 people a year are killed in rollovers. When vehicles roll, their 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. Stronger roofs also can prevent occupants, especially those who aren't using belts, from being ejected through windows, windshields, or doors that have broken or opened because the roof has deformed. Roofs that don't collapse help keep people inside vehicles as they roll.
Any vehicle can roll over in a crash, but the problem is worse in some kinds of vehicles than others. About 25 percent of occupant deaths in crashes of cars and minivans involve rolling over. This proportion jumps to 59 percent in SUVs.
The best way to prevent the deaths is to keep vehicles from rolling over in the first place. Electronic stability control is significantly reducing rollovers, especially fatal single-vehicle ones (see "ESC reduces multiple-vehicle crashes as well as single-vehicle ones," June 13, 2006). When vehicles do roll, side curtain airbags help protect the people inside. Belt use is essential.
In the Institute's roof strength test, a metal plate is pushed against one side of a roof at a constant speed. To earn a good rating, the roof must withstand a force of 4 times the vehicle's weight before reaching 5 inches of crush. This is called a strength-to-weight ratio. For an acceptable rating, the minimum required strength-to-weight ratio is 3.25. A marginal rating value is 2.5. Anything lower than that is poor.
The small SUVs that did well in the Institute's new test have roofs that are 2.5 to 3.5 times stronger than the minimum federal safety standard for roof strength. The National Highway Traffic Safety Administration has proposed a new standard, but it wouldn't be as tough as the Institute recommends.
"Our research shows that a strength-to-weight ratio of 4 reflects an estimated 50 percent reduction in the risk of serious and fatal injury in single-vehicle rollover crashes compared with the current federal standard of 1.5," Lund explains.
A good roof strength rating will be a new requirement to earn the Institute's Top Safety Pick award for 2010. This is the second time criteria for this award have been tightened since the first winners were announced in 2005 (see "Top Safety Pick: 13 vehicles are cream of the crop for 2007," Nov. 21, 2006). Availability of electronic stability control became a requirement starting with 2007s.
"Adding Top Safety Pick criteria means we'll see fewer winners in 2010," Lund says. A record 73 vehicles have qualified for the 2009 award so far, and 8 of the 2009 winners are among the 12 small SUVs the Institute just tested for roof strength. However, only 3 of the 8 — Tiguan, Forester, and Element — have the roof strength to qualify for next year's award.
Next the Institute will assess roof strength of mini and midsize cars.