The Insurance Institute for Highway Safety is an independent, nonprofit research organization whose mission is to reduce automobile deaths, injuries, and property damage. On July 3rd, IIHS released results of its rear impact studies for 2007 vehicles. In short -- trucks didn't perform very well.

Rear impact studies examine seat and head restraints to determine how the two systems mesh. Ideally, the head restraint should work in unity with the seat during a rear impact, keeping the head and neck in line with the torso as it lunges forward. To do that, the IIHS recommends that head restraints be at least as tall as the head's center of gravity and as close to the back of the head as possible. Studies have shown that restraints positioned 4-inches or more behind the head are more likely to result in whiplash injury during a rear impact.

Dummies used in tests have head and torso heights equal to an "average" adult male. Adjustable head restraint positions are considered only if the headrest locks in those positions, but vehicles lose points for requiring people to make adjustments, because most drivers and passengers don't bother.

2007 Trucks Rated "Good"

• Toyota Tundra

2007 Trucks Rated "Acceptable"

• Nissan Titan
• Dodge Dakota
• Mitsubishi Raider

2007 Trucks Rated "Marginal"

• Toyota Tacoma
• Chevrolet Colorado
• GMC Canyon
• Isuzu i-series

2007 Trucks Rated "Poor"

• Ford F-150
• Dodge Ram 1500
• Chevy Silverado & Silverado Classic
• Nissan Frontier
• Ford Ranger
• Mazda B Series

Studies rated 17 of 59 SUVs as "good," compared to 6 out of 44 in 2006. The IIHS feels the improvement is partly due to the number of newly designed vehicles being released, but not all of the new models fared well in tests -- the new Mazda CX-7 and CX-9 both fell into the "marginal" category.

Should you care about the studies? Although they can happen any time, rear impacts are most common during in-town driving. If the majority of your driving is in a town or city, in busy traffic, put test results on your comparison list when it's time to shop.

More Reading: IIHS guidelines for rear impact crashes

_{Toyota Tundra Photo © Dale Wickell}