ARLINGTON, VA - The Insurance Institute for Highway Safety has given Top Safety Pick awards to the 2011 Cadillac CTS and Infiniti M37/M56, after the vehicles performed exceptionally well in roof strength tests that assess how well vehicles would protect people in rollover crashes.

The 2011 Cadillac CTS and Infiniti M37/M56 drew "good" ratings -- the highest given by IIHS -- in all four institute safety evaluations. Moreover, they have electronic stability control -- a requirement for the Top Safety Pick designation.

Meanwhile, the IIHS said that the 2010 Lexus GS and Audi A6 were rated "acceptable," and the 2010 Acura RL was rated "marginal" for rollover protection.

"The test results show that manufacturers are moving quickly to improve the rollover safety of their newest designs," said IIHS President Adrian Lund.

The BMW 5 series, Hyundai Genesis, Lincoln MKS, Mercedes E class and Volvo S80 also are Top Safety Pick winners in the large luxury class, based on test results released earlier.

The IIHS evaluates rollover protection using a roof strength test. In this test, a metal plate is pushed against one corner of a vehicle's roof at a constant speed. The maximum force sustained by the roof before five inches of crush is compared to the vehicle's weight to find the strength-to-weight ratio. According to IIHS, this process provides a good assessment of vehicle structural protection in rollover crashes. "Good"-rated vehicles have roofs that can withstand a force equal to at least four times the vehicle's weight.