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Status Report, Vol. 36, No. 4 | April 28, 2001 Subscribe

New head restraint rule would prevent many whiplash injuries

The head restraints in most cars are inadequate, neither high enough nor close enough to many people's heads to prevent whiplash injuries or associated neck disorders in crashes. Now a proposed upgrade of the federal safety standard covering head restraints would impose new geometric requirements expected to improve restraint effectiveness.

The mandate for higher head restraints would bring U.S. rules in line with height requirements of the tougher European standard. In addition, the U.S. rule would require head restraints to be close to occupants' heads. Several studies have shown that an effective restraint must be close to the head horizontally as well as vertically.

"The proposed revisions should result in fewer whiplash injuries," says Institute president Brian O'Neill. "Overall the proposal would greatly strengthen a standard that was weak when it was first issued over 30 years ago."

High enough and close enough

Current federal rules require head restraints to be adjustable to a height 27½ inches above a vehicle's so-called seating reference point, defined by a test machine placed in the seat. But when head restraints are adjusted to this height, they aren't high enough to protect many adult occupants from whiplash injuries. Restraints left in the lowest, or "down," position often are 2 to 4 inches lower than 27½ inches. This means the restraints are of no benefit to most people.

Furthermore, most car occupants don't adjust their head restraints. Research shows they leave the restraints in the "down" position. The proposed new rule would mandate restraints at 29½ inches above the seating reference point even when unadjusted. The backset, or distance between the back of an occupant's head and the front of the head restraint, would be limited to two inches.

BioRID's segmented neck and flexible spine are more like a human's than the neck and spine of Hybrid III, designed for frontal testing. Another rear impact dummy option is RID2 which, like BioRID, has a segmented neck and spine but not as many joints.

Two compliance options

Manufacturers may demonstrate compliance with current head restraint requirements by static testing — that is, by meeting certain measurement criteria — or by demonstrating a certain level of performance in a dynamic sled test. The proposed rule would maintain these options, a decision that's opposed by the Institute and others. Although a dynamic test could encourage automakers to develop active head restraint systems that deploy on impact, the proposed test option could have unintended negative consequences.

A problem is that average-size and larger male Hybrid III dummies would be used in the test, and "dynamic tests with dummies representing heavy adult males could result in active restraint designs that don't work for lighter occupants, especially women, who are most at risk of whiplash injury," explains Adrian Lund, the Institute's chief operating officer.

Head restraints

Head restraints come in a variety of shapes and sizes. The ones that provide the most effective protection against whiplash injury extend to the top of an occupant's head and fit close to the back of the head.

Quest is on for new test procedures

Whatever their size, the Hybrid III dummies present a problem in testing whiplash risk because their rigid spines don't interact with vehicle seats the way people's spines do. The Institute and others, including Volvo, recommend the development of a dynamic test using crash dummies especially designed to measure the parameters most predictive of whiplash injury risk. In fact, the Institute is a member of a newly formed working group, the International Insurance Whiplash Prevention Group, to develop dynamic test procedures to evaluate and compare different seat/head restraint designs.

Right now at least two test dummy designs appear more appropriate than Hybrid III. BioRID, or biofidelic rear impact dummy, was designed by a consortium of Chalmers University in Sweden, restraint manufacturer Autoliv, Saab, and Volvo to study relative head/neck motion in rear crashes. BioRID's spine is composed of 24 vertebra-like pieces. Its neck moves more like a human's, compared with the Hybrid III neck, and its segmented spine interacts with vehicle seats in a more humanlike way. BioRID II is in production from Denton ATD, a U.S. manufacturer that collaborated with Chalmers to develop the dummy.

A second dummy, RID2, is another possibility for rear impact testing. Originally developed by a European consortium led by TNO, a Dutch research group, this dummy has been taken over by First Technology Safety Systems, a U.S. company that expects a production version of RID2 in May.

"The development of an appropriate dynamic test procedure will require additional time and effort, and we think it's better to wait than go with a test procedure with possible deleterious consequences," Lund says. "Meantime, we strongly support the government's proposal to require better head restraint geometry, which research indicates would significantly reduce whiplash injuries among both women and men."

Global whiplash group works on standard

An international group of researchers is working to develop procedures for dynamic head restraint tests.

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