• Aug 21, 2009
IIHS microcar roof tests - Click above for high-res image gallery

The Insurance Institute for Highway Safety has just tested the latest batch of the smallest cars on the market to determine the strength of their roofs in the event of a rollover accident. Coming out on top with a "good" rating was the Smart Fortwo, which isn't all that surprising – due in large part to the runabout's diminutive size, Daimler put lots of effort into the design of its so-called Tridion safety cell.

Somehow, we're equally as unsurprised that the Chevy Aveo scored the lowest of the six automobiles tested. Chevy's least expensive car earned a "marginal" rating from the Institute. Sitting in between those two bookends were the Honda Fit, Hyundai Accent, Mini Cooper, and Toyota Yaris, all of which scored "acceptable" ratings.

It's interesting to note that the Smart Fortwo fared quite a bit better in this kind of test than in the Institute's series of frontal offset crash tests versus a Mercedes-Benz C-Class sedan. Click past the break for the official press release.



[Source: Insurance Institute for Highway Safety]

PRESS RELEASE:

Smart Fortwo rates good for roof strength; test is designed to assess & compare occupant protection in rollover crashes


ARLINGTON, VA - The Smart Fortwo has the strongest roof and the Chevrolet Aveo has the weakest among 2009 micro and minicars recently tested by the Insurance Institute for Highway Safety. The Smart earns the highest rating of good compared with acceptable for the Honda Fit, Hyundai Accent, Mini Cooper, and Toyota Yaris. The Aveo is rated marginal.

The rating system is based on Institute research showing that occupants in rollover crashes benefit from stronger roofs. Vehicles rated good must have roofs that are more than twice as strong as the current minimum federal safety standard requires. The ratings, products of the Institute's new roof strength testing program, add to consumer information tests that rate vehicles for front, side, and rear crashworthiness. The roof test is designed to help consumers pick vehicles that will help protect them in rollover crashes.

"We anticipate that our roof strength test will drive improved rollover crash protection the same way our frontal offset and side tests have led to better occupant protection in these kinds of crashes," says Institute president Adrian Lund.

Roofs have gotten stronger during the past few years, Institute research shows. Part of the reason is that automakers have made structural improvements to earn better front and side ratings in Institute tests. Strong A and B pillars help prevent intrusion in these types of crashes. They also help hold up the roof.

"Small cars should have an easier time with the roof strength test," Lund explains. "Their light weight means their roofs don't have to work as hard to keep the structure around the occupants intact in a rollover."

About 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 of injury from contact with the roof itself. Stronger roofs also can prevent people, especially those who aren't using safety belts, from being ejected through windows, windshields, or doors that have broken or opened because the roof deformed. Roofs that don't collapse help keep people inside vehicles as they roll.

The best protection is to keep vehicles from rolling in the first place. Electronic stability control is significantly reducing rollovers, especially fatal single-vehicle ones. When vehicles do roll, side curtain airbags help protect people. Belt use is essential.

How roofs are evaluated: In the Institute's test, a metal plate is pushed against 1 side of a roof at a constant speed. To earn a good rating, a 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 ratio is 3.25. A marginal rating value is 2.5. Anything lower than that is poor.

"Compared with the current federal standard of 1.5, a strength-to-weight ratio of 4 reflects an estimated 50 percent reduction in the risk of serious or fatal injury in single-vehicle rollover crashes," Lund explains.

The Smart withstood a force of 5.4 times its weight. The Aveo withstood a force of just over 3 times its weight.

Cars have been built to meet the same roof crush standard, Federal Motor Vehicle Safety Standard 216, 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 pickup trucks are heavier, so they're exempt.

New federal requirements: In April the National Highway Traffic Safety Administration ended numerous delays by unveiling a new rule that doubles the current roof strength requirement (strength-to-weight ratio of 1.5) for vehicles with weight ratings up to 6,000 pounds. Roofs on vehicles with weight ratings 6,000 to 10,000 pounds will be required to withstand a force equal to 1.5 times their unloaded weight. Another requirement is that roofs maintain sufficient headroom during testing. For the first time, the government also will require the same performance on both sides of the roof when tested sequentially. Phase-in begins in September 2012, and all vehicles must comply by September 2016.

"The federal government's leisurely phase-in of the new standard means roofs won't have to get stronger right away," Lund says, "so we plan to continue rating vehicle roof strength for the foreseeable future. We want to reward manufacturers who are ahead of their competition when it comes to providing protection in rollover crashes. We want to help consumers identify the safest vehicle choices."

Roof ratings added to award criteria: 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. Availability of electronic stability control became a requirement starting with 2007s.

"Adding roof strength to Top Safety Pick criteria means we're going to see fewer winners in 2010," Lund points out. A record 84 vehicles have qualified for the 2009 award so far
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    • 1 Second Ago
  • 13 Comments
      • 5 Years Ago
      How do you get marginal in this test if you're above what is federally mandated?

      • 5 Years Ago
      So it withstands more than double what is required, but that isn't enough? How much weight do they need to add to these things? They are supposed to be cheap, so lightweight strong materials aren't much of an option, and this thing already weighs more than cars from 10 years ago.

      Also, does this factor in which is more likely to flip?

      How about a better overall rating that factors in likelyhood to flip along with likelyhood of injury from flipping. Not to mention: Why do we still care about people stupid enough not to belt themselves in?
      • 5 Years Ago
      Is the Aveo, a micro car?????? wtf?
      • 5 Years Ago
      Oh, great. It comes out on top for roof strength in the case of a rollover.

      But what about a frontal collision, you ask? For your consideration: http://www.youtube.com/watch?v=6dDUiX-VnME

      • 5 Years Ago
      Ooooh, that Aveo looks awfully safe...wouldn't want to be caught dead in one of those, although from those pics I probably would be if I rolled one.
      • 5 Years Ago
      Needs moar and bigger pillars.

      What's a little visibility when you have side air bags?
      • 5 Years Ago
      I don't see a rating for it on the IIHS site and it's not really a microcar. However, I would rate the roof stregth for the New Beetle very high. As I rolled my 2000 NB 3.75 times and it came out with far less damage then the cars in the IIHS test.
      • 5 Years Ago
      Not that surprising really. Smart knows its car is at a size disadvantage and has put a lot of work into their 'tridion' safety cell to make it stronger than most.
        • 5 Years Ago
        It's important to remember in this test, the score is a factor of the car's weight. The smart's small size works for it because since it weighs less, its roof must support less weight to do well in the test. So it cannot be extrapolated just from the rankings order that the smart's roof is stronger than all of the other cars' (though it really is), but rather that it's stronger in relationship to the car's weight. If something fell on you, it COULD be a diferent story. For example, in this test group the Toyota ranks 2nd in roof strength as a ratio of the car's weight, but the Hyundai's roof should be able to handle the 2nd heaviest load after the smart (the Hyundai is by a good bit the heaviest car of the group and its factor is close to the Toyota's).
        • 5 Years Ago
        In addition, this is a case where the Smart's smaller size helps with it's structural rigidity.
      • 5 Years Ago
      Aveo is a micro car???? wtf
      • 5 Years Ago
      More of that legendary GM attention to detail Lutz goes on about.

      Realistically the Aveo is actually a much more functional and practical car than the Smart either way though that isn't saying much. Personally I wouldn't want to drive either one. Hopefully the new Aveo is a vast improvement over this current "Korean Cavalier". Though it is hard to imagine how it couldn't be. Unfortunately GM still has a pretty decent stock of these turds to clear through before we ever see the new one.
      • 5 Years Ago
      If only the Aveo had some redeeming feature that made it OK to take the risk... but, it doesn't.
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