After controlling for driver age, gender, vehicle type and weight, the analysis concluded that a driver of a vehicle that received a "good" IIHS rating for driver protection in a side impact is 70 percent less likely to die in a left-side crash, compared with a driver of a vehicle rated "poor." A driver of a vehicle rated "acceptable" is 64 percent less likely to die, and a driver of a vehicle rated "marginal" is 49 percent less likely to die.
"When we first developed and began conducting these tests, we were able to draw conclusions about what kinds of improvements needed to be made in the vehicles in order to make them more safe in crashes," said David Zuby, IIHS chief research officer. "It was our feeling that doing these tests, and providing these ratings, would help prompt the carmakers to introduce new designs that would make vehicles safer.
"But it took a few years for enough real-world crash data to become available to do the analysis we just did. It took time for enough of the vehicles we rated to have been in crashes before we could reach these conclusions about survival rates in real-world crashes that involved those vehicles."
Drivers Only, Airbags Mandatory
In its analysis, IIHS used databases compiled by state and local police departments and by the National Highway Traffic Safety Administration. Figures were calculated using ratings that only reflect driver-side protection, so they are different than the ratings the Institute has already published -- which reflect protection for both the driver and a passenger. The reason the recent analysis looked mainly at driver risk is that federal crash statistics don't contain enough data for the Institute to be able to calculate passenger risk in the same fashion, said Zuby.
Side-impact crashes accounted for 27 percent of passenger-vehicle occupant deaths in the United States in 2009. These crashes can be especially deadly, because the sides of vehicles have relatively little space to absorb energy in a way that protects occupants. In its analysis, the Institute only used data from real-world crashes that involved IIHS-rated vehicles that were equipped with standard side airbags to protect both the head and torso. Previous research and testing has established the critical importance of side airbags, and no vehicle without head-protecting side airbags has ever earned a "good" rating, Zuby said.
In the Institute's testing, a vehicle is hit on the driver side by a deformable barrier weighing 3,300 pounds and traveling at 31 mph. The barrier's height and shape are designed to approximate the front of a typical SUV or pickup truck. Ratings are based on the "injury measurements" recorded on the crash-test dummies, as well as by measuring head protection and vehicle intrusion.
One significant factor in determining ratings in the Institute's side-crash-tests is the type of dummies used. Instead of just using dummies that are the height of an average-sized male, the Institute also uses a smaller dummy – one that is five feet tall – in order to represent a small women or 12-year-old child. The choice of a small-female dummy was a first for any consumer-information crash test, said Zuby. The decision to also use smaller dummies is that that women are more likely than men to suffer serious head injuries in real-world side impacts.
Today, 78 percent of current vehicle designs that have been tested by the Institute have "good" side ratings -- compared with only about a third of the vehicles tested when the Institute began its side-crash-test ratings in 2003.
"We do believe that auto manufacturers have paid attention to our ratings, and to NHTSA's ratings, and made improvements as a result, because they know that consumers want safe cars," said Zuby. "When they design a vehicle that receives a good rating from us, they're able to use that safety rating in their ads for that vehicle."
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