By DEE-ANN DURBIN, AP Auto Writer Thu Aug 16, 6:42 AM ET

DETROIT - The 2008 BMW 5 Series was the worst performer in new side-impact crash tests of luxury sedans by the insurance industry.

The Acura RL, Kia Amanti and Volvo S80 all earned the highest safety rating from the Insurance Institute for Highway Safety, according to results released Thursday. The Cadillac STS and Mercedes E-Class earned the second-highest rating.

The tests were designed to show what would happen if a truck or sport utility vehicle hit the side of the sedan at 31 mph, the speed of a serious crash. Side-impact crashes are the most common type of fatal crash after a frontal crash, killing around 9,000 people on U.S. roadways in 2005, the institute said.

"Growing sales of SUVs and pickups have exacerbated height mismatches among passenger vehicles, thereby increasing the risks to occupants of many vehicles struck in the side," Insurance Institute President Adrian Lund said in a news release.

All six sedans were equipped with standard side air bags. The air bags in the BMW 5 Series protected the head, but separate air bags designed to protect the chest and abdomen performed poorly, the institute said.

BMW spokesman Thomas Plucinsky said the institute's test indicated the 5 Series has a strong body structure but the dummy was injured when it was hit by the arm rest. Plucinsky said BMW does up to 12 crash tests on all its cars as well as computer simulations of crashes.

"The issue is that depending on the location of seat, the location of dummy, the location of the sled, the results could change," he said. "This was one test on one day on one car."

The Kia Amanti was one of the lowest priced sedans in the group, with a starting price of around $25,500, but it offered greater protection than more expensive entries. The BMW 5 Series starts at $43,500, while the Mercedes E-Class starts at $50,550, according to automotive research site Edmunds.com.

"The Amanti shows that you don't have to buy an expensive car to get good protection in crashes with SUVs and pickups," Lund said.

The Volvo S80 also won the institute's top safety award for overall crash protection, since it got the highest ratings in front, side and rear crash tests and has electronic stability control as standard equipment. Stability control helps prevent rollovers. The 2007 Volvo S80 starts at $47,350, according to Edmunds.

All of the sedans tested were 2007 models except the 5 Series, which was redesigned for 2008, institute spokesman Russ Rader said.

The Volvo S80 also won the institute's top safety award for overall crash protection, since it got the highest ratings in front, side and rear crash tests and has electronic stability control as standard equipment