You're driving along, minding your own business, when the brake lights of the car in front of you gleam red, indicating an abrupt slowdown in the flow of traffic. Responding quickly with the brake pedal, you've got enough distance between your car and the next to avoid a collision. But the tailgater behind you isn't as lucky, and his front bumper comes hurtling into the rear of your vehicle.
The jolt from such an impact can cause your head to jerk back and forth like a bobble-head doll, leaving you stuck with more than just a damaged vehicle. Even minor accidents can leave you with whiplash, a condition affecting the ligaments and muscles of the neck and shoulders, typically caused by rear-end collisions. Whiplash can cause lasting distress and discomfort, but a properly configured head restraint system can reduce or even prevent such an injury.
So what exactly are head restraints? They are what most people think of as headrests, but that's not their primary function. Head restraints are designed to restrict head movement during a rear-impact collision and reduce the chance of neck and shoulder injury. They're an important (though often overlooked) safety feature that has been federally mandated in front seating positions since 1969.
Most vehicles contain manually adjustable head restraints, and current legislation governs their placement with the intent of maximizing safety. Under federal law, head restraints must be adjustable from no lower than 29.5 inches to at least 31.5 inches above an occupant's hip. In line with studies that have shown that restraints are most effective when they are close to your noggin, restraints are also required to sit no farther than 2 inches from the back of an occupant's head.
It's important to remember that this regulation was implemented on September 1, 2008, and only applies to 2009 passenger vehicles built on or after this date. Similar legislation was in place prior to this, but it was less comprehensive. If your car was built before the law took effect, you need to take special care to make sure that the restraints are properly adjusted.
Research has shown that most drivers with adjustable head restraints don't take the time to configure them properly, leaving them at their lowest setting. The result? The restraints are rendered ineffective, since those left "down" on cars built before the new law took effect are typically 2-4 inches lower than the current federal regulations dictate. In the event of an accident, unadjusted restraints provide little or no protection against neck injuries.
But how should these restraints be adjusted? According to the National Highway Traffic Safety Administration (NHTSA), to be effective, the top of the restraint should lie somewhere between the top of your ears and the top of your head. If the restraint articulates for horizontal adjustment, it should be placed so that it's as close to your head as possible, without pushing your head forward or causing the height of the restraint to drop. The position of your seatback is also important — less is better when it comes to reclining. A more upright seatback means that the head restraint will likely be in a safer position — one that's closer to your head.
Though manually adjusted head restraints are part of the package on most vehicles, there are alternative setups. Some vehicles offer restraint systems that adjust automatically with changes in seat position; others offer systems that adjust dynamically in a crash. Of the three types of restraints available — manual, automatic and dynamic — some studies have shown that dynamic restraint systems (also known as active head restraints) tend to offer the best protection from neck injury in a crash.
Dynamic head restraint systems take an active approach to injury prevention; they're designed to deploy automatically in the event of an accident. They also reduce the whiplash-inducing abrupt motion of the head and torso that can take place during a collision by utilizing more than just head restraints. The seatback is also incorporated into this system, creating a mechanism that cradles and supports the head and torso in the event of a sudden impact.
Volvo and Saab have been pioneers when it comes to dynamic head restraint systems, and virtually all of their recent models have featured this safety technology. The key component in Volvo's Whiplash Injury Prevention System (WHIPS) is a hinge at the base of the seatback. This hinge yields and partially rotates when an occupant's torso makes the sort of impact associated with a rear collision, moving the seatback rearward and thus reducing forward motion of the torso.
WHIPS also features a fixed head restraint with effective geometry, meaning it sits high and close to the head; this restraint catches the head in an accident, enabling it to move forward with the torso. Reduced torso acceleration and the head restraint's quick reduction of head movement mean that the neck changes shape less — and the change occurs more slowly — in the collision than with a conventional seatback/head restraint. The result? Whiplash is less likely to occur.
Saab's Active Head Restraint (SAHR) is based on the lever principle. A padded head restraint is linked to a pressure plate inside the seatback. When a rear-end collision causes the torso to make impact with the seatback, force is exerted on the plate. This sends the head restraint moving up and forward, enabling it to catch the occupant's head before the motion that induces whiplash has a chance to begin. Additionally, the seatbacks themselves feature crossbars and padding designed to absorb crash energy and cradle an occupant's torso, reducing differential movement between the head and torso.
The designers over at Saab clearly recognize an important point: Seatbacks can play a big part in protecting you from whiplash injury. Studies have shown that cars with softer seating do a better job of keeping passengers safe from whiplash; ideally, a seat should be pliable enough to soak up the energy of a rear-end collision. Stiffer seats — like the sport seating found in many performance cars — often have the opposite effect. Your shoulders are likely to bounce off them in a crash, leading to injury.
An excellent resource in your effort to evaluate head restraint systems is the information offered by the Insurance Institute for Highway Safety (IIHS). This organization rates head restraints using a two-step evaluation system. In the first step, the head restraint's geometry is rated — evaluators look at the placement of the restraint, including its distance behind and below the head. In the second step, restraints are evaluated in a crash test format using a specially designed dummy.
So the next time you get into your car or consider buying a vehicle, give some thought to the head restraints perched atop those seatbacks. They could very well wind up saving your neck someday!