IIHS Adds Roof Strength Test to Small Cars

Following up on the roof strength tests applied to small crossovers and SUVs earlier this year, the Insurance Institute for Highway Safety (IIHS) is now applying its new testing procedure on a handful of subcompact cars. The IIHS hopes that the new test, which is much more demanding than the government’s future requirements, will further increase vehicle safety by making vehicle rollovers more survivable. With its new test just ramping up, the Institute tested six of the smallest cars available in the United States (Chevrolet Aveo, Honda Fit, Hyundai Accent, MINI Cooper, smart fortwo and Toyota Yaris) raising the total number of vehicles tested now up to 18. Of the vehicles tested by the IIHS, all of them passed the current governmental standards for roof strength, but only the 2009 Smart fortwo walked away with the most impressive roof safety.

Current governmental roof standards date back to 1973 requiring a roof strength-to-weight ratio of only 1.5 – meaning that the roof must withstand a weight one and a half times the vehicle’s total weight – and does not apply to bigger vehicles such as pickup trucks and SUVs. Although the NHTSA proposed strengthening its standards to double the current amount (and not excluding passenger vehicles weighing more than 6,000 pounds), the IIHS method is much more aggressive in an attempt to save more lives. To attain the Institute’s “Good” rating, a vehicle’s roof must withstand a force of four times the weight of the vehicle, applied directly to the driver’s side of the vehicle to the A- and B-pillars, before reaching five inches of crush, and the new roof ratings will become required criteria to attain the coveted Top Safety Pick starting in 2010. According to the IIHS, 10,000 people die each year in rollover accidents as a result of the roof deforming and crushing into the passenger compartment.

The only vehicle that was able to pass the new test from the IIHS with a “Good” rating was the new fortwo which trades size for a safety cell that is designed to dissipate crash energy. Not surprisingly, this safety cell also plays a key role in both side-impact protection and roof strength. The IIHS and the National Highway Traffic Safety Administration (NHTSA) have already given the fortwo top marks in this category, and now the IIHS shows that the car is also superior when it comes to roof strength and rollover safety (which is ironic because of the fact that according to the NHTSA and its three-star rollover rating, the Smart fortwo has one of the largest likelihoods of rolling over for all passenger cars). The Smart fortwo even surpassed the Institute’s rating by attaining a roof strength-to-weight ratio of 5.4.

For vehicles to earn an “Acceptable” rating for roof strength, the roof must have a minimum roof strength-to-weight ratio of 3.25 or be able to withstand a force of 3.25 times the weight of the vehicle. The four vehicles that received this rating are the Honda Fit, Hyundai Accent, MINI Cooper and Toyota Yaris, but the Yaris and the Accent aren’t that far away from a “Good” rating with roof strength-to-weight ratios of 3.7. It isn’t clear which Yaris or Accent models were tested since both are available as either a sedan or a hatchback.

The only vehicle of this bunch to receive a “Marginal” rating was the Chevrolet Aveo sedan which had a roof strength-to-weight ratio of 3.0 – double what the NHTSA currently requires and just below the IIHS’ threshold for an “Acceptable” rating. None of the vehicles tested this time around were given a “Poor” rating which is anything with a roof strength-to-weight ratio less than 2.5.

After a record number of vehicles made the Institute’s list of the safest vehicles on the road, it now plans to include the roof strength test to earn a coveted spot as an IIHS Top Safety Pick. Las November, the Institute released a list of 72 vehicles that made the list for 2009, and that list continues to grow with new vehicles such as the 2010 Ford Taurus and 2010 Honda Insight joining the party. The new roof strength test will help narrow down the field as evidenced by the fact that of the 18 vehicles tested so far for roof strength, 10 of them were already Top Safety Picks, but following the test, only three (Subaru Forester, Volkswagen Tiguan and Honda Element) will remain Top Safety Picks for 2010. Of the small cars tested, only the Honda Fit was a 2009 Top Safety Pick, but with its “Acceptable” rating, it appears it will not be joining the list for 2010.

The IIHS’ president Adrian Lund hopes that this new testing procedure will motivate automakers to go above and beyond what is required by the NHTSA by rewarding manufacturers that are safety leaders and helping consumers to identify the safest vehicles on the road.

"The federal government's leisurely phase-in of the new standard means roofs won't have to get stronger right away," Lund said. “Our new roof strength ratings are going to drive improvements in rollover crash protection the same way our front- and side-crash tests have led to more crash-rated vehicles.”