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Status Report, Vol. 36, No. 9 | October 6, 2001 Subscribe

Head restraintsGeometry improves, and some have advanced designs

Head restraints can protect our necks in crashes, and the Institute's latest round of ratings of the restraints in more than 200 passenger vehicle models indicates these devices are getting better. For the first time, more than half of all new passenger vehicles offer restraints that are rated good or acceptable.

About 30 percent of vehicles have head restraints rated good. Another 25 percent have acceptable head restraints. Such restraints should reduce the risk of whiplash injury by meeting positioning requirements in relation to drivers' heads — that is, the restraints would be positioned high enough and close enough to the backs of occupants' heads in a rear-end crash to mitigate neck injury.

There's a dramatic comparison between these results with those from the 1995 model year, when the Institute began evaluating head restraints. It was almost impossible to find a good head restraint in a 1995 model. Those in just five cars were rated good, and three of the five cars were Volvo models (see "How bad are they? Best head restraints are in Volvo models; restraints in 117 of 164 cars rated poor," Sept. 16, 1995).

By the 1997 model year, good and acceptable head restraints were easier to find but still in fewer than one-fourth of the cars in which Institute researchers measured head restraint geometry (see "How bad are they? Only five passenger vehicles have head restraints with good geometry; more than half of the restraints are poor," April 12, 1997). Among 1999 models, fewer than a third of the restraints measured were rated good or acceptable (see Status Report special issue: neck injuries in rear-end crashes, May 22, 1999).

"More and more automakers are finally getting the message," says Institute chief operating officer Adrian Lund. "In 1995, unless you were short it was hard to find a car with a head restraint high enough to provide protection. But now, even taller people have a good chance of getting head restraints that will protect them. This marks a sea change."

Head restraints are improving not only in cars but also in sport utility vehicles and pickup trucks, though good and acceptable restraints aren't in more than half of these vehicles. Forty-eight percent of 2001 model SUVs and 50 percent of pickups offer head restraints rated good or acceptable. Comparable proportions for 1997 models are 13 percent (SUVs) and 21 percent (pickups).

Head restraint improvements 1995, 1997, 1999, and 2001 models

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Ratings begin with restraint geometry

A necessary first step to lessen whiplash injury risk in a rear-end crash is a head restraint that can be positioned behind and close to the back of an occupant's head. These two criteria — the height of a head restraint and its backset — form the basis of the Institute's rating system.

The top of a restraint ideally should be as high as the top of an occupant's head. The backset, or distance between the back of an occupant's head and the front of the head restraint, should be as small as possible. The Institute rates most head restraint designs good, acceptable, marginal, or poor based on how a restraint meets these two criteria for an average male.

Active restraints earn good ratings

The restraints in some vehicles are active. That is, they're designed to move into position during a rear impact. Such head restraints are rated good by both the Institute and the Research Council for Automobile Repairs, a consortium of international research centers. The automatic good ratings will continue until comparative dynamic tests for whiplash protection are available. The Institute and others are planning such tests.

"We're crediting the advanced systems and giving them good ratings until we have a dynamic test protocol in place," Lund says. "Our testing to date indicates such ratings are warranted."

For example, in 1999 the Institute crash tested a 1999 Saab 9-5 with an active head restraint design, finding low risk of neck injury. Saab recently published its own study comparing crash outcomes in models with and without active head restraints, reporting much lower whiplash injury rates in cars with active systems. Other advanced designs feature seatbacks that control the acceleration of an occupant's torso in a rear-end crash. However, these designs don't automatically earn good ratings.

Who's offering advanced designs?

Saab's active restraint and General Motors "catcher's mitt" design both feature a head restraint that moves up and forward as an occupant's torso loads the seatback in a rear-end collision. All Saabs since the 1999 model year have such restraints, as do current Buick LeSabre, Pontiac Bonneville, and Oldsmobile Aurora models. Nissan offers a similar active head restraint design in its Maxima and Infiniti I30, Q45, and QX4 models.

While active seatback designs don't automatically qualify for good ratings, they do control the acceleration of the torso, which is thought to be important in reducing whiplash injuries. Volvo, which equips all of its models with fixed head restraints rated good, also installs a whiplash injury prevention system — the seatback yields and partially rotates when loaded by an occupant's torso in a rear impact. This design is intended to reduce the forward acceleration of the torso, so even the limited relative head/torso movement that's allowed by Volvo's good head restraint occurs more gradually than with a conventional seatback.

Toyota's advanced design, called the whiplash injury lessening system, includes a seatback designed with a strong outer frame and little or no cross bracing behind the shoulder blades. In a rear impact, the force applied by the seatback to an occupant's torso is controlled by the foam and other materials that make up the cushioning in the seatback.

Saab and General Motors feature similar seatback designs with their active head restraint systems. In addition, these two automakers include some geometric and cushion specifications that direct occupants downward as they sink into their seatbacks in a rear-end collision, thus counteracting the "ramp up" that has been described in tests with volunteers (an occupant's neck shortens as the torso "ramps up" the seatback and then lengthens during rebound).

Need for dynamic testing

Good head restraint geometry doesn't guarantee good occupant protection in rear-end crashes, but it's an important first step. As more restraints with good geometry are introduced and the number of active head restraint systems increases, there's a need for dynamic testing to assess the overall performance of seats and head restraints in reducing whiplash injury risk. An international insurer group is developing a dynamic test to be used for standard evaluations (see accompanying story, this page). As a member of this group, the Institute will be conducting dynamic tests once it acquires the necessary testing device.

"It's encouraging to track all the manufacturer activity aimed at improving head restraints," Lund says. "Generally speaking, restraints are getting higher and closer to the head, and many more adjustable restraints now come with locks to keep them in position. These improvements, together with the introduction of active head restraints and other advanced designs, bode well. We hope they lead to a decrease in the incidence of whiplash injuries."

How they've improved: Some head restraints have better geometry, others are active designs

1995 Taurus head restraint
2001 Taurus head restraint

Improved geometry: Some vehicle models that used to have head restraints rated poor now are being equipped with good or acceptable restraints. For example, the head restraints in older Taurus models (1995 model, above left) weren't high enough to protect many occupants from whiplash injury. (The measuring device in the vehicle seat is the size of an average male.) In contrast, the restraints in 2001 Taurus models (above right) extend higher and fit closer to the back of the head.


SAAB head restraint

Advanced designs: More and more new cars are being equipped with active head restraints like those in 1999 and later model Saab 9-5s (left) that automatically move up and closer to occupants' heads in rear-end collisions. These restraints automatically earn good ratings. Other advanced head restraint designs in newer models feature seatbacks that control the acceleration of an occupant's torso in a rear-end crash but, unlike active head restraints, these don't automatically earn good ratings.

SIDEBAR
How head restraints are rated

Geometry is the basis for most head restraint ratings under an international protocol.

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