Only 6 of the seat/head restraint combinations in 44 current model SUVs are rated good for protection against whiplash injuries in rear-end crashes. None of the seat/head restraint designs in 15 pickup truck models earns a good rating. Overall 4 out of 5 SUV and pickup seat/head restraints recently evaluated by the Insurance Institute for Highway Safety are rated marginal or poor for whiplash protection. This is the first time the Institute has tested SUV and pickup seats using a dummy that can measure forces on the neck during a simulated rear-end crash. 

Only the seats in the Ford Freestyle, Honda Pilot, Jeep Grand Cherokee, Land Rover LR3, Subaru Forester, and Volvo XC90 models earn good overall ratings. Among those earning poor ratings are seat/head restraints in popular models such as the Chevrolet TrailBlazer, Ford Explorer, and Toyota 4Runner SUVs plus the Chevrolet Silverado pickup truck and some seats in Ford F-150 and Dodge Dakota pickups.

"Manufacturer advertising often emphasizes the rugged image of SUVs and pickups," says Institute president Adrian Lund. "However, the Institute's evaluations show seats and head restraints in many models wouldn't do a good job of protecting most people in a typical rear impact in everyday commuter traffic."

The Institute evaluates seat/head restraints in two stages. First restraint geometry is measured to determine its height and distance behind the back of the head of an average-size man. Seats with good or acceptable head restraint geometry then are tested dynamically on a movable platform using a dummy that measures forces on the neck. This sled test simulates a collision in which a stationary vehicle is struck in the rear by a vehicle of the same weight going 20 mph. Seats without good or acceptable geometry are rated poor overall because they cannot be positioned to protect many people in rear-end crashes.

Head and torso must move together

When a vehicle is struck in the rear and driven forward, the vehicle seats accelerate occupants' torsos forward. Unsupported, an occupant's head will lag behind the forward movement of the torso. This differential motion causes the neck to bend back and stretch. The higher the torso acceleration, the more sudden the motion, the higher the forces on the neck, and the more likely a neck injury is to occur.

"The key to reducing whiplash injury risk is to keep the head and torso moving together," Lund explains. "To ensure they move together, a seat and head restraint have to work in concert to support an occupant's neck and head, accelerating them with the torso as the vehicle is driven forward. To accomplish this, the geometry of the head restraint has to be adequate, and so do the stiffness characteristics of the vehicle seat."

A head restraint should extend at least as high as the center of gravity of the head of the tallest expected occupant. A restraint also should be positioned close to the back of an occupant's head so it can contact the head and support it early in a rear-end crash.

If a head restraint isn't positioned behind an occupant's head, it cannot support the head in a rear impact, but good restraint geometry by itself isn't sufficient. A seat also has to be designed so its head restraint doesn't move backward in a rear impact because this would prevent the restraint from catching the head.

At the same time, a vehicle seat cannot be too stiff. It has to "give" so an occupant will sink into it, moving the head closer to the restraint. The evaluation criteria take into account both static geometry and the dynamic performance of the seats and head restraints together in the test.

Geometry is improving

The Institute doesn't test seats with head restraints that are rated marginal or poor for geometry. These seats automatically earn a poor rating overall because their head restraints cannot be positioned to protect many taller people.

"It's encouraging that only 12 of the 58 seat/head restraint combinations we evaluated didn't make it to the testing stage because of marginal or poor geometry," Lund says. "The auto manufacturers have been working to improve this aspect of head restraint design."

Rear-end collisions are frequent, and neck injuries are the most common serious injuries reported in automobile crashes. They account for 2 million insurance claims each year costing at least $8.5 billion. Such injuries aren't life-threatening, but they can be painful and debilitating.