There are a lot more cars at the top of the test ranks at both the Insurance Institute for Highway Safety (IIHS) and the National Highway Transportation Safety Administration (NHTSA) as computer designs, internal crash testing, and superior materials combine to make our cars safer than ever. The latest to join the ranks are the Saab 9-5 and Volkswagen CC.
To earn a Top Safety Pick, cars must meet "good" levels, the IIHS' best rating, in all crash testing including roof crush tests, plus offer standard stability control.
Other cars recently tested for roof strength include the 2011 Lexus ES 350, which scored "good" in roof tests, but didn't achieve a Top Safety Pick due to "marginal" rear-impact scores. The Infiniti G, Lexus IS, and BMW 3-Series were also tested, but only scored "acceptable" in roof crush tests.
Roof strength is measured by slowly crushing the structure until it deforms by five inches. The force required to move that much metal is compared to the car's weight, yielding a strength-to-weight ratio. If it's high enough, it earns a "good" rating.