A tweak earlier this year to the head restraint design of General Motors Corp.'s midsize cross/utility vehicles help the quartet earn a “Top Safety Pick” from the Insurance Institute for Highway Safety.

The insurance group's highest safety ratings for the GMC Acadia, Saturn Outlook, Buick Enclave and newly launched Chevrolet Traverse arrived less than a week after two of the auto maker's small CUVs performed poorly in the same tests.

The Chevrolet Equinox and its Pontiac Torrent platform mate scored poorly because GM does not offer side airbags as standard equipment on the vehicles, which the IIHS classifies as small SUVs. GM notes the Equinox will add the feature with the '09 model year and the IIHS intends to conduct another test later this year.

Scrutiny of crashworthiness in the segment also arrives at a critical time. Although auto makers will make stability control standard on all light vehicles under 10,000 lbs. (4,537 kg) by the '12 model year, according to National Highway Traffic Safety Admin. rules, consumers are suddenly flocking from fullsize and midsize body-on-frame trucks to the midsize and small CUV segments for better fuel economy.

And while NHTSA provides crash-test ratings for all vehicles and recently revamped its testing and scoring process, the changes will not take effect until '10 model-year testing. That said, many industry observers still consider the IIHS tests more severe and its scoring more easily understood by consumers. For example, '08 and '09 model Acadias receive the group's highest rating of “good” in front-, side-, and rear-impact crash exercises.

The Acadia's score also benefits from standard electronic stability control, which the IIHS includes in its evaluations as a means to push greater adoption of the technology ahead of NHTSA's deadline. Acadia models dating back to '07 receive the all-around good score.

But only Enclave and Outlook models built after March 2008, when GM added a slight design enhancement to the vehicles' head restraints, receive an all-around “good” score. Auto makers must install either active head restraints, which move forward in a rear-end crash to prevent whiplash, or static restraints, which reduce the distance between the head and the headrest through shear girth, by 2009.

The GM midsize CUVs use a static head restraint. A big backer of more robust head-restraint technology, the IIHS publishes regular reports on the effectiveness of various head-restraint systems.

In the frontal-crash test, the IIHS reports “well-controlled” dummy-movement inside GM's midsize CUVs. After the dummy moved forward into the frontal airbag, the IIHS says, its head contacted a driver side curtain airbag that deployed during the exercise. A passenger side-curtain airbag also deployed.

“That's a good thing,” says IIHS spokesman Russ Rader. “When side airbags deploy in a front crash it can keep your head and arms inside the car. It doesn't always occur, but more auto makers are tuning them to deploy in a frontal crash.”

Ford Escape Tops Insurance Institute Crash Test; Chevy Equinox Poor Performer