Last month the National Highway Traffic Safety Administration (NHTSA) told automakers the head restraints in their passenger vehicles will have to extend higher and fit closer to the backs of people's heads. The Institute has been asking the agency for years to issue such a standard because too many head restraints still are designed too low and too far behind the head to provide adequate support. When a vehicle is rear-ended with sufficient force that an occupant's torso is pushed forward by the vehicle seat, the head has to be supported to keep moving along with the torso. If it isn't supported, it will lag behind until it's pulled forward by the neck. This motion can cause whiplash injury.
"Automakers already have been making progress with their head restraint designs, and this new standard will lock in the improvements. It also will require automakers who haven't made improvements to do so. Then every passenger vehicle will be equipped with head restraints with good geometry," says Institute chief operating officer Adrian Lund.
The standard establishes a minimum of 29.5 inches from an occupant's hip to the top of a head restraint. Before this, there was no minimum. Head restraints had to be adjustable to 27.5 inches. And for the first time the new standard addresses the distance behind the head, referred to as backset. Head restraints will have to be within about 2 inches behind the head.
Effective beginning with 2009 models, these requirements will apply to head restraints in the front seats of vehicles, which are mandated. If the back seats are outfitted with head restraints, they'll have to meet the same requirements for height and backset.
Long wait for the new rules
The head restraint standard in effect until the 2009 model year is the same one that has been in effect since such restraints first were required in 1969.
"It was a weak standard to begin with," Lund points out. "Since then NHTSA has talked about upgrading it but has taken this long to do it."
In 1974 NHTSA proposed an upgrade but then let it drop. The agency later began a new rulemaking and proposed a substantial upgrade in 2001. It took nearly four years to get from there to the standard announced last month.
Meanwhile, there have been improvements outside the regulatory process, largely in response to Institute ratings of head restraint geometry published since 1995 (see Status Report special issue: whiplash injuries, Sept. 16, 1995). Back then nearly all restraints were rated poor for geometry. In recent model years more than half are rated good.
Institute ratings vs. new federal rule
Head restraint geometry is rated from good to poor according to this protocol. Many restraints rated poor meet the old federal requirements, but soon such restraints will have to be higher and closer to the head.
Geometry is the first step
A head restraint with inadequate geometry cannot begin to protect many taller people from neck injury in rear-end crashes. Still, good geometry alone isn't enough. The vehicle seat is important too. It has to be designed so it won't rotate backward in a rear impact, which would move the attached head restraint away from an occupant's head. A seat also has to allow an occupant to sink into it, moving the head closer to the restraint.
Last year the Institute joined with insurance groups internationally to add dynamic tests to evaluate how well seats and head restraints work together to reduce neck forces. The first round of evaluations found few passenger vehicles with good dynamic test results (see Status Report special issue: protection against neck injury in rear crashes, Nov. 20, 2004). The seat/head restraints in 8 vehicles are rated good, but those in 54 other vehicles are poor.
NHTSA does offer auto manufacturers the option of complying with the new standard by conducting a dynamic test with a Hybrid III dummy representing an average-size man.
"It's a good thing for NHTSA to consider dynamic performance, but the test shouldn't replace the requirements based on geometry," Lund says, "because the test won't ensure adequate protection for people who are taller than an average-size man. Besides the Hybrid III dummy isn't designed for rear testing. What's needed for protection from whiplash is a restraint with good geometry plus good dynamic performance, not one or the other."