Smart Fortwo rates best of the Minis and Micros for roof strength in IIHS tests. [fimg=right]http://www.cleanmpg.com/photos/data/501/Driving_SMART_-_in_front_of_the_Pacific_Ocean_in_San_Francisco_News.jpg [/fimg]Wayne Gerdes - CleanMPG - Aug. 19, 2009 The attention getting Smart Fortwo overlooking the Pacific - Starts at $11,990 and achieves a 36 mpg combined rating per the 08 EPA. The Smart Fortwo has the strongest roof and the Chevrolet Aveo has the weakest among 2009 micro and minicars tested by the Insurance Institute for Highway Safety (IIHS). The Smart earns the highest rating of Good compared with acceptable for the Honda Fit, Hyundai Accent, Mini Cooper, and Toyota Yaris. The Aveo was rated marginal. The Smart Fortwo also tested higher than all but one of the 13 small SUVs previously tested by IIHS. Roof strength is the most important vehicle attribute for protecting occupants in a rollover crash according to IIHS. 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. "Small cars should have an easier time with the roof strength test. 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. Roof evaluations In the IIHS’ roof crush test, a metal plate is pushed against one 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. According to the IIHS, the Smart Fortwo withstood a force of 5.4 times its weight during the tests, far exceeded the minimum required force ratio of 4 times the vehicle’s weight to earn a “Good” rating. The IIHS reports that a vehicle in the “Good” category has 50 percent less risk of serious or fatal injury in a single-vehicle rollover crash. As IIHS makes clear, when it comes to roof strength for rollover protection, lightweight vehicles fare better because “their roofs don’t have to work as hard to keep the structure around the occupants intact…” In April the National Highway Traffic Safety Administration (NHTSA) 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. 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. In addition, the smart fortwo already exceeds the new federal roof strength requirements that will not start phasing in until 2012, with all vehicles needing to comply by 2016. Engineers designed the smart to be a trendsetter in safety of small cars, with a high level of standard technologies that eclipse federal mandates. The Smart Fortwo’s Tridion safety cell, which surrounds and protects vehicle occupants, is a reinforced steel cage that acts like a race car roll cage, and is the primary reason the Smart Fortwo performed so well in the IIHS roof strength test.