Dr. Harold Byers, Jr., B.A., M.S., D.C.
Neck injury risk is lower if seats and head
restraints are rated good. Neck sprains and strains, commonly known as whiplash, are the most
frequently reported injuries in U.S. insurance claims. In 2007, the cost of
claims in which neck pain was the most serious injury was about $8.8 billion, or 25
percent of the total payout for crash injuries.
Head restraints help prevent whiplash. When a vehicle is struck from the rear, the
seatback pushes against an occupant's torso and propels it forward. If the head is
unsupported, it lags behind the torso until the neck reaches its limit, and the head
suddenly whips forward. A good head restraint prevents this by moving an occupant's
head forward with the body during a rear-end crash.
Head restraints should be properly adjusted. The top of the head restraint
should be even with the top of the head or, if it won't reach, as high as it will go. The
distance from the back of the head to the restraint should be as small as possible.
The rate of neck injury complaints is 15 percent lower in cars and SUVs with seat/head
restraint combinations rated good compared with poor. The results for serious injuries
are more dramatic. Thirty-five percent fewer insurance claims for neck injuries lasting 3
months or more are filed for cars and SUVs with good seat/head restraints than for ones
These are the main findings of a new Institute study of thousands of insurance claims
filed for damage to vehicles, all 2005-06 models, that were struck in front-into-rear
impacts. Conducted in cooperation with State Farm and Nationwide, the study is the first time seat/head restraint ratings based on dynamic tests conducted by the Institute
have been compared with real-world neck injury results.
"In stop-and-go traffic, you're more likely to get in a rear-end collision than any other
kind of crash, so you're more likely to need your seat and head restraint than any other
safety system in your vehicle," says David Zuby, the Institute's senior vice president for
vehicle research. "This is why it's so important to fit vehicles with seats and head
restraints that earn good ratings for saving your neck."
The Institute has been measuring and rating head restraint geometry since 1995. The
higher and closer a restraint is, the more likely it will be to prevent neck injury in a rear
collision. In 2004 the Institute added a dynamic test simulating a rear crash to refine
the ratings. Vehicles are rated good, acceptable, marginal, or poor based on both
restraint geometry and test results (see Status Report special issue: protection against
neck injury in rear crashes, Nov. 20, 2004). The same rating system is used
internationally by a consortium of insurer-sponsored organizations, the International
Insurance Whiplash Prevention Group.
An estimated 4 million rear collisions occur each year in the United States.
or strain is the most serious injury in one-third of insurance claims for injuries in all
kinds of crashes. The annual cost of these claims exceeds $8 billion annually.
While findings about real-world neck injury in vehicle seats rated good and poor are
clear, those for seats rated acceptable and marginal aren't as clear. There wasn't any
reduction in initial neck injury complaints for acceptable and marginal seats, compared
with poor, though long-term neck injuries were reduced.
"The long-term injuries are the very ones we want to reduce because they're the most
serious," Zuby points out. "While many neck injuries involve moderate discomfort that
goes away in a week or so, about one of every four initial complaints still was being
treated three months later. These longer term injuries involve more pain and cost more
to treat. They're being reduced about one-third in vehicles with seat/head restraints
rated good compared with poor. Serious neck injuries also are being reduced in seats
that are rated acceptable or marginal.
More and more passenger vehicles are being equipped with seats and head restraints
When the Institute started evaluating and comparing the geometry of the
head restraints in 1995 model cars, only a handful were rated good and 80 percent were
poor. Then the automakers responded, and by 2004 about 4 of every 5 head restraints
had good or acceptable geometry (see Status Report special issue: protection against
neck injury in rear crashes, Nov. 20, 2004). Similarly, the dynamic performance of
seat/head restraint combinations is improving. Only 12 percent of 2004 model cars had
combinations rated good, but by the 2007 model year the proportion had increased to
29 percent (see "Head restraints are improving but not fast enough," Aug. 4, 2007).
These improvements are being driven not only by ratings of seat/head restraints
published by the Institute and other insurer-sponsored groups but also by a U.S.
standard that will require the restraints to extend higher and fit closer to the backs of
people's heads by the 2009 model year.
In the United States, automakers also have been spurred by the Institute's TOP SAFETY PICK award. To win this designation, a vehicle
has to earn good ratings in all three tests — front, side, and rear.
How the injuries occur
When a vehicle is struck in the rear and driven forward, its seats accelerate occupants'
torsos forward. Unsupported, an occupant's head will lag behind this forward torso
movement, and the differential motion causes the neck to bend 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.
Injuries in rear crashes
These vehicles didn't sustain a lot of damage when they were struck from behind, but
the drivers were treated for injuries suffered in the impacts. Neck sprains and strains are
the most serious problems reported in about 1 of 3 insurance claims for injuries. This
problem could be reduced by equipping vehicles with seat/head restraints rated good,
based on Institute tests. Twenty-nine of all recent model cars and 22 percent of other
passenger vehicles have systems rated good for protection against neck injury.
Factors that influence neck injury risk include gender and seating position in addition to
the designs of seats and head restraints. Women are more likely than men to incur neck
injuries in rear crashes, and front-seat occupants, especially drivers, are more likely to
incur such injuries than people riding in back seats are.
The key to reducing whiplash injury risk is to keep an occupant's head and torso moving
together. To accomplish this, the geometry of a head restraint has to be adequate — high
enough and near the back of the head. Then the seat structure and stiffness must be
designed to work in concert with the head restraint to support an occupant's neck and
head, accelerating them with the torso as the vehicle is pushed forward.
About the study..... To correlate seat/head restraint ratings with real-world neck injury risk, researchers
studied about 3,000 insurance claims associated with rear crashes of 105 of the 175
passenger vehicles (2005-06 models) for which the Institute has ratings based on both
restraint geometry and seat performance in dynamic tests. The claims were filed with
State Farm Mutual Insurance and Nationwide Insurance, which together account for
more than 20 percent of the personal auto insurance premiums paid in the United
States in 2005. The researchers modeled the odds of a neck injury occurring in a rear-
struck vehicle as a function of seat ratings (good, acceptable, marginal, or poor), while
controlling for other factors that also affect neck injury risk, such as vehicle size and
type and occupant age and gender.
The percentage of rear-struck drivers with neck injury claims was 16.2 in vehicles with
seats rated good, based on dynamic testing. Corresponding percentages were 21.1 for
seats rated acceptable, 17.7 for marginal seats, and 19.2 for poor ones. Neck injuries
lasting 3 months or more were reported by 3.8 percent of drivers in good seats, 4.7
percent in acceptable seats, 3.6 percent in marginal seats, and 5.8 percent in seats rated
"What these data show is that we're pushing seat designs in the right direction," Zuby
says, "Results for acceptable and marginal seats weren't as clear as for good seats. Initial
neck injury claims weren't significantly lower than for poor seats. Still we saw
reductions in claims for serious neck injuries in acceptable and marginal seats as well as
in good ones."
This is the third study the Institute has conducted that indicates the superiority of
seat/head restraint combinations rated good for reducing neck injury risk. In 1999 the
Institute found that head restraints rated good for geometry alone had lower insurance
claims for neck injuries. In 2003, Institute researchers expanded the data, finding that modern features such as head restraints that automatically adjust in rear-end collisions
and seats that absorb energy also reduce insurance claims.