Whiplash and Neck Injury Information Page

Whiplash Question and Answers Page


Thanks to Insurance Institute for Highway Safety
for permission to reproduce this page!

as of March 2004

  1. What is whiplash?

  2. What happens to an occupant when their vehicle is struck from the rear?

  3. How common are neck injuries? Are motorists susceptible to neck injuries in all crash configurations?

  4. Why does my vehicle have a headrest? Are there restraint standards?

  5. How should my head restraint be positioned?

  6. How good are the head restraints on passenger vehicles?

  7. Are the Institute's restraint ratings reflected in real world crashes?

  8. What factors influence the severity of neck injury?

  9. What restraint improvements can be expected in the future?

  10. Is there any evidence head restraint improvements are effective in reducing neck injuries?

1. What is whiplash? Whiplash and whiplash-associated disorders (WAD) are terms used to describe a range of neck injuries that are related to sudden distortions of the neck. The most common symptom whiplash victims report is pain due to mild muscle strain or minor tearing of soft tissue. Other injuries include nerve damage, disc damage, and in the most severe cases, ruptures of ligaments in the neck and fractures of the cervical vertabrae. Generally, minor whiplash injuries are associated with pain and decreased range of motion in the head and neck. These symptoms usually last only a short time, but occasionally they last longer and include headaches, dizziness, and tingling in the arms. People experiencing whiplash injuries report symptoms that last from a few hours to several years with the vast majority experiencing short-term symptoms of pain. The physical injury to create symptoms of whiplash is uncertain. It is suspected that the biological cause of long-term whiplash symptoms is nerve damage while short-term pain may be a minor strain or sprain.

It is known that people can experience severe crashes with no neck injury if there is little or no movement of the head relative to the torso. Consequently, neck distortion resulting from sudden movement of the head relative to the torso probably explains most whiplash injuries. Hyperextension of the neck, or distortion beyond its normal range of motion, may explain many whiplash injuries, but experimental and field studies suggest that nerve damage and its associated long-term symptoms can occur with milder levels of neck distortion. One hypothesis that explains these nerve injuries is based on damage to the nerves in the joints caused by motion of adjacent neck vertebrae during a crash. [1] Another hypothesis suggests that the nerve damage is caused by fluctuation in spinal fluid pressure arising from neck distortions. [2]

2. What happens to an occupant when their vehicle is struck from the rear? While whiplash injuries are common in all types of crashes, motorists involved in rear-end crashes are more likely to experience whiplash. When a vehicle is struck from the rear it is accelerated forward, causing the seatback to push against the occupant's torso and propel it forward. The head lags behind the torso until the neck reaches its limit of distortion, then the head is suddenly accelerated by the neck much like the tip of a whip, hence the term whiplash. Head restraints limit the neck distortion that occurs before the head starts to follow the torso.

head motion diagram

3. How common are neck injuries? Are motorists susceptible to neck injuries in all crash configurations? In the United States, neck sprains and strains are the most frequently reported injury in insurance claims. In 1997, it is estimated that 66 percent of all insurance claimants under bodily injury liability coverage and 59 percent under personal injury protection coverage -- the two most important insurance injury coverages -- reported a minor neck injury. For 42 and 36 percent of injury claimants, respectively, neck sprains or strains was the most serious injury reported. The cost of just these injury claims where neck pain was the most serious was $7 billion. [3]

Whiplash injuries can occur in any kind of crash but occur most often in rear-end collisions. A 1999 Institute study found that 26 percent of rear-struck vehicle drivers reported neck injuries. [4] This was essentially the same as the 24 percent neck injury rate reported in a 1972 Institute study. [5] Estimates of neck injury rates in other studies have ranged from 7 to 37 percent, depending on whether police or motorists reported the information. [6, 7, 8]

4. Why does my vehicle have a headrest? What many motorists refer to as a headrest is actually a head restraint. It is a common misconception that a restraint is a comfort feature and this simply is not true. Head restraints are installed in vehicles for safety purposes and are an essential safety feature like lap/shoulder belts. Effective head restraints reduce the rearward motion of an occupant's head in a rear-end crash and decrease the likelihood of sustaining a whiplash injury. A recent 2002 Public Attitude Monitor asked participants what the main purpose of a head restraint was and 67 percent correctly identified safety while 13 percent said comfort and another 15 percent didn't know. [9]

Are there restraint standards? Yes, since January 1, 1969, the National Highway Traffic Safety Administration under FMVSS (Federal Motor Vehicle Safety Standard) No. 202 has mandated head restraints in the front outboard seats of all new passenger cars. On September 1, 1991, head restraint standards were extended to pickups, vans and SUVs. The restraints installed by manufacturers must extend at least 27.5 inches above the seating reference point (a point slightly above and in front of where the seat and seatback meet) when in their highest (up) positions. Even at this height the restraint isn't high enough for many occupants. Many motorists do not adjust their restraints yet there is no regulation dictating a minimum height for restraints in the lowest (down) position in the United States. The European Economic Community followed the United States and mandated head restraints in the late 1970s. Recently the European Union adopted more stringent standards. Effective in 1998 head restraints have to be at least 29.5 inches in the lowest position and exceed 31.5 inches in the highest position. The United States proposed in 2001 to upgrade its standard but the rule has not yet been finalized. In the meantime, two types of restraints satisfy the current requirements. The first is an integral head restraint; this design has a seatback that is high enough to meet the head restraint height requirement. The second is an adjustable head restraint, which consists of a cushion that is attached to the seatback by sliding metal shafts. Adjustable restraints can be moved and sometimes locked into different heights; some can also be adjusted horizontally to change the distance between the head and restraint. Manufacturers may install either integral or adjustable restraints.

5. How should my head restraint be positioned? To reduce the likelihood of sustaining a whiplash injury in a crash, neck distortion must be kept to a minimum. Well-designed and properly positioned head restraints are essential to whiplash prevention. A head restraint should be positioned at least level with the top of the ears or about 3.5 inches below the top of the occupant's head. The distance from the back of the head to the restraint should be as small as possible, preferably less than four inches. Because motorists differ in height, the amount of adjustment needed varies. For some occupants no adjustment from the downward position is required.

6. How good are the head restraints on passenger vehicles? The Institute regularly evaluates the geometry of head restraints in hundreds of new passenger vehicles and has been doing so since 1995. Each restraint is classified into one of four geometric zones defined by its height and backset (distance from the back of an occupant's head to the front of the restraint). Restraints are rated as good, acceptable, marginal, or poor. The measurements are made with a dummy representing an average-size male at a typical seatback angle. Head restraints have improved since the surveys began. In 1995 only 3 percent of measured head restraints rated good compared with 45 percent in 2003. The number of poor restraints has decreased dramatically from 82 percent in 1995 to 10 percent in 2003. These ratings are a good indicator of the proportion of motorists likely to be protected in a rear-end crash. Marginal head restraints are not more than 4.5 inches from the back of the dummy's head and are tall enough to protect average-size males and shorter motorists from injury. Restraints rated acceptable and good can protect taller motorists.

The head restraint dummy shown at left is fully assembled for measurements. A score is assigned from the measurements using the table shown (above left). Manufacturers have been improving their head restraints over time, as shown in the graph above.

7. Are the Institute's restraint ratings reflected in real world crashes? Yes, Institute ratings are related to how well people are protected in real world rear-end crashes. The Institute analyzed more than 5,000 insurance claims and determined that, all other factors being the same, drivers with restraints rated good are 24 percent less likely than drivers with poor head restraints to sustain neck injuries in rear-end crashes. In vehicles with restraints rated as acceptable, insurance claims for neck pain were lower for females but not for males. This may be because females in general are shorter than males, allowing a restraint in the down position to offer some protection to women. [4] A second Institute study conducted in Rochester, New York, surveyed 585 drivers who had been in rear-end crashes. Measurements were taken while each driver assumed a normal driving posture with their restraint in the position it was during the crash. The findings showed that head restraints positioned at or above the head's center of gravity could reduce reported neck pain after a rear-end crash. Drivers with such head restraints reported 40 percent fewer instances of neck pain than those with poorly positioned restraints. [10]

8. What factors influence the severity of neck injury?

Height: Height is a risk factor, particularly among women, according to recent German research. [11] Often times shorterindividuals are protected by an unadjusted head restraint. Stature may not play a role in the severity of injury to men because many head restraints are too low to offer even shorter men protection. Taller motorists who don't adjust their head restraints are more likely to sustain whiplash injuries.

Gender: The same German report also found women to be 1.8 to 2.2 times more at risk of neck injury in all types of collisions, a finding that is consistent with research by the Institute and other organizations. In addition, a Swedish study found that women with whiplash injuries are more likely to develop long-term symptoms of whiplash than are men with whiplash. Fifty-five percent of the women who sustained whiplash injuries went on to develop long-term symptoms compared with 38 percent of men. [12] One possible explanation is that men have more neck musculature than women for about the same size head. Another hypothesis is that women tend to sit farther away from their seatbacks than men, thus their heads travel farther to the rear in a crash before reaching a head restraint.

Seating position: It is uncertain which seating position exposes an occupant to a greater chance of sustaining a neck injury. One study concluded drivers have a higher risk rate than passengers. It was hypothesized that drivers are prone to move forward and away from the seatback as they reach for the steering wheel and observe traffic around them, whereas passengers are usually more relaxed and lean further back in their seats, with their heads close to the restraint. Occupants seated in the back seat rather than the front, are also less likely to sustain a neck injury. [13]

A more recent study indicates a higher disability risk from neck injury for females than for males in any seating position. For females, the disability risk is lowest in the front passenger seat. The risk is significantly higher for females in the rear passenger seat. For men, there is a small difference between the front seat occupants, while the risk decreases from the front seat to the rear seat. The disability risk in the driver seat is three times higher for females than for males, and four times higher for females in the rear seat. [14]

9. What restraint improvements can be expected in the future? After years of neglect, improved head restraints are beginning to appear. Some auto manufacturers include head restraints that automatically adjust position when the seat is adjusted. Tall occupants who adjust the seat rearward to gain leg room also gain the added protection of a higher head restraint. Other manufacturers have incorporated 'active' systems that automatically improve head restraint position during a crash. For example, the Saab Active Head Restraint and General Motors Catcher's Mitt designs include head restraints attached to a lever arm in the seatback that moves the restraint up and forward as the occupant's back pushes into the seatback. Volvo's WHIPS -- or whiplash injury prevention system seat - combines good head restraint geometry with a special seatback hinge that gently accelerates the seat occupant's torso, thus giving the head restraint time to catch the head before neck distortions become too severe.

Volvo WHIPS seat:

Saab Active Head Restraint

10. Is there any evidence head restraint improvements are effective in reducing neck injuries? Recently the Institute gathered data from Nationwide, Progressive, and State Farm insurance companies to look at improved seat design in rear-end crashes. More than 2,000 property damage liability claims were identified involving selected vehicles. The vehicles studied were the Ford Taurus and Mercury Sable models with improved head restraint geometry, Volvo S70s with WHIPS (Whiplash Injury Prevention System), Toyota and Lexus models with the WIL (Whiplash Injury Lessening) system plus a number of Buick, Nissan, Pontiac, and Saab models with active head restraints. The rates of insurance claims for driver neck injuries in the rear-end crashes were compared before and after the seat and head restraint design changes. A 43 percent reduction in neck injury claim rates was seen for the Saab, General Motors, and Nissan models with active head restraints, compared with similar cars before such restraints were introduced. Similar before/after comparisons of Volvos and Fords showed reductions in claim rates. A 49 percent reduction was seen in Volvos compared with an 18 percent reduction in the Fords with improved geometry. The Toyota WIL system did not show any reduction in neck injuries. [15]

  1. Ono, K. and Kaneoka, K. 1997.
    Motion analysis of human cervical vertebrae during low-speed rear impacts by the simulated sled.
    Proceedings of the 1997 International IRCOBI Conference on the Biomechanics of Impact, 223-237.
    Bron, France: International Research Council on the Biokinetics of Impacts.

  2. Svensson, M.Y.; Aldman, B.; Lövsund, P.; Seeman, T.; Suneson, A.; and Örtengren. 1993.
    Pressure effects in the spinal canal during whiplash extension motion -- a possible cause of injury to the cervical spinal ganglia.
    Proceedings of the 1993 International Conference on the Biomechanics of Impacts, 189-200. IRCOBI, Lyon, France.

  3. Insurance Research Council. 1999.
    Injuries in auto accidents.
    Malvern, PA: Insurance Research Council.

  4. Farmer, C.M.; Wells, J.K.; and Werner, J.V. 1999.
    Relationship of head restraint positioning to driver neck injury in rear-end crashes.
    Accident Analysis and Prevention, 31: 719-728.

  5. O'Neill, B.; Haddon, W.; Kelley, A.B.; and Sorenson, W.W. 1972.
    Automobile head restraints -- frequency of neck injury claims in relation to the presence of head restraints.
    American Journal of Public Health 62: 309-406.

  6. Braunstein, P.W. and Moore, J.O. 1959.
    The fallacy of the term 'whiplash' injury.
    American journal of surgery, 97: 522-529.

  7. Quinlan, K.P.; Annest, J.L.; Myers, B.; Ryan, G. and Hill, H. 2004.
    Neck strains and sprains among motor vehicle occupants -- United States, 2000.
    Accident Analysis and Prevention 36: 21-27.

  8. States, J.D.; Balcerak, J.C.; Williams, J.S.; Morris, A.T.; Babcock, W.; Polvino, R.; Riger, R.; and Dawley, R.E. 1972.
    Injury frequency and head restraint effectiveness in rear-end impact accidents.
    Proceedings of the 16th Stapp Car Crash Conference, 228-245.

  9. Insurance Research Council. 2002.
    Public Attitude Monitor 2002.

  10. Chapline, J.F.; Ferguson, S.A.; Lilis, R.P.; Lund, A.K.; and Williams, A.F. 2000.
    Neck pain and head restraint position relative to the driver's head in rear-end collisions.
    Accident Analysis and Prevention 32(2): 287-297.

  11. Temming, J. and Zobel, R. 1998.
    Frequency and risk of cervical spine distortion injuries in passenger car accidents: significance of human factors data.
    Proceedings of the International Conference on the Biomechanics of Impact 219-233.
    Goteborg, Sweden, IROCBI.

  12. Krafft, M. 1998.
    A comparison of short- and long-term consequences of AIS 1 neck injuries, in rear impacts.
    Proceeding of the International Conference on the Biomechanics of Impact, 235-248.
    Goteborg, Sweden, IRCOBI.

  13. Lundell, B.; Jakobsson, L.; Alfredsson, B.; Jernstrom, C.; and Isakkson-Hellman, I. 1998.
    Guidelines for and the design of a car seat concept for improved protection against neck injuries in rear end car impacts.
    SAE Technical Paper Series 980301. Detroit, MI: International Congress and Exposition.

  14. Krafft, M.; Kullgren, A.; Lie, A.; and Tingvall, C. 2003.
    The risk of whiplash injury in the rear seat compared to the front seat in rear impacts.
    Traffic Injury Prevention 4: 136-140.

  15. Farmer, C.M.; Wells, J.K.; and Lund, A.K. 2003.
    Effects of head restraint and seat redesign on neck injury risk in rear-end crashes.
    Traffic Injury Prevention 4: 83-90.

1996-2004, Insurance Institute for Highway Safety, Highway Loss Data Institute

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