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Rear-Facing Bracing and Tethering

Properly used, rear-facing child restraints have proven to be extremely effective in actual crashes, and experience in Sweden has shown that children through the age of 3 can benefit as well.  These large rear-facing child restraints sit away from the vehicle seatback to give the child more leg room and have an additional strap or other device to prevent rearward rotation.  These restraints have extremely low injury and fatality rates, with estimates of injury-reduction effectiveness as high as 96% when compared to the unrestrained child.  (The above link is a pdf file and require Adobe Acrobat.  It will load slowly)


The idea of using a rear-facing restraint braced and tethered is fairly new in the United States (US), and little testing has been done to prove or disprove any benefit that may be gained from doing so.  However, rear-facing restraints in Sweden are installed and used in this manner, and have shown great benefit and protection to children up through the age of four.  Although the Swedish restraints are significantly larger then US restraints, there are a few US restraints that can be used in this manner, notably the Britax Roundabout and Advantage.  The Safeline Sit-N-Stroll also has the ability to tether rear-facing, but there are several "disadvantages" with this seat that would prevent it from being used in this manner, namely it's low rear-facing weight limit and necessity to be re-installed for each use.  It has been noted by respected researcher Kathleen Weber that a braced and tethered rear-facing restraint may provide superior protection, but the benefits will be gained by older and heavier infants and toddlers...perhaps beginning at 9 months or so. 

The principle behind tethering and bracing a rear-facing restraint is that the restraint that is most closely "coupled" to the vehicle will provide the most benefit in terms of "ride-down" for the child.  That is, the child will be able to ride down the crash completely with the crushing vehicle, experiencing a minimum of crash force and decreasing the chance for severe injury.  Not all crashes are survivable, and even the most "optimal" of restraint cannot protect against all injury, especially in severe crashes. 

Most Child Passenger Safety experts believe that while a braced seat may provide some extra protection in a frontal crash, the tether provides more benefit to a child in a side impact or rear-offset crash. 

Rear-facing Britax restraints may be tethered either toward the front of the vehicle, down toward the floor, or the rear of the vehicle to an existing tether anchor.  The tethered/braced rear-facing restraint is tethered toward the front and braced against the front seat.  Theoretically, the bracing eliminates the downward rotation of the restraint, and the tether eliminates the "rebound".

Information on tethering Britax convertibles, including how to find an anchor position for the tether connector strap.  This site offers pictures and lots of helpful information.


Pictures demonstrating a tethered, braced restraint


Crash test footage various restraints


Notes From SafetyBeltSafe USA

On Bracing

There are three reasons behind the theory of positioning a rear-facing restraint against a structure in front of it (back of front seat, or instrument panel if no air bag):

1. It will keep the restraint in a more upright orientation during a crash, which helps keep the child from ramping up the back, loading the shoulders into the straps, and possibly allowing the head to rise over the top of the restraint.

2. If the rear-facing restraint is in initial contact with a vehicle structure, the child will directly ride down the crash with the crushing vehicle, which reduces the deceleration forces (and injury potential) to the child. This is standard practice for large rear-facing restraints in Sweden.

3. During a frontal crash, an unsupported restraint will move forward and rotate down toward the impact point. Unless there is a large gap (varies with each restraint, seat, crash, but perhaps 10 inches) between the restraint top and whatever is in front of it, there will likely be contact anyway. This hit will be harder and transfer more impact force to the child than the situation in #2 above. It is also more likely to result in restraint breakage.

If the gap is small or the child is on the heavy side, it is much better to be already touching any forward structure prior to a crash than to hit it during the crash. Resting against a forward seatback is only one way to achieve these benefits. Another is a tether designed to be routed rearward (Australian method) to limit forward rotation, which one manufacturer (Britax) currently provides.


On Rear-Facing Tethers

Only a few child restraints in the U.S. have tethers for rear-facing use, but these are common in some other countries. Australia has tethered the top of infant restraints to an anchor positioned behind the vehicle seat for many years, and the most popular rear-facing "capsule" will not work properly if it is not tethered. Australians have also generally kept infants rear-facing until only about 6 months, when they start to use a forward-facing and virtually-always tethered restraint. Tethering a rear-facing CR toward the rear of the vehicle, which describes the Australian method, limits the downward rotation of the restraint and child during a frontal crash but does nothing to affect initial stability, rebound, or rear-impact.

Sweden has always used rear-facing restraints for children up to 4 years old, when they are moved directly into boosters with lap-shoulder belts. These large rear-facing restraints, which are set several inches away from the vehicle seatback to provide leg room, must rest against a vehicle structure, such as the instrument panel (unless there is an air bag) or the back of the front seat to keep them from falling over. Since the CR and its occupant can be tall and heavy, the Swedes have also tethered the backs down to the floor to eliminate rearward rotation during rebound or rear impact. The Swedes also have some small infant-only restraints that are not tied to the floor but do use the shoulder portion of the lap-shoulder belt to wrap around the "front" (the child's back) of the restraint to limit rotation during a crash. This installation method is used throughout Europe for frontal crash protection, but there is little effect on rebound or rear-impact motion.

The first U.S. infant restraint, which is the model for subsequent ones, did not use a tether in either direction nor a shoulder belt, but it worked very well. During development, the engineers observed that it turned over toward the vehicle seatback after a crash test and, largely in order to justify what happened anyway, they called this the "cocoon effect." There was also some justifiable concern that the small infant's neck might be injured on rebound or rear-impact unless the restraint were allowed to freely rotate in this direction. Justified or not, this concept has remained and seems to make intuitive sense. The counter-argument that the infant's head will "slam" into the seatback and be injured on rebound has not been validated in nearly 30 years of accident experience.

Britax, which has operations in Australia, Sweden, UK, and Germany, as well as in the U.S., devised a means to tie a traditional U.S. rear-facing convertible down to the base of the front seat structure to give it a firm installation and help the parent achieve something close to a 45° back angle, or more upright as appropriate. This tether does achieve a very secure installation, which is reassuring for parents, but it does little, if anything, to improve protection in a frontal crash. Downward rotation will likely be limited more by the back of the front seat than by any cushion compression achieved with a tight downward tether. Another concern is that parents may use the tether to make the CR too reclined.

The restraint models on which this is offered, however, can accommodate a child up to 30 lb rear facing, and for this usage the limit on rebound or rear-impact motion may be beneficial. Although crash experience indicates that rebound of infant-only restraints in frontal impacts does not cause serious injury, similar movement of a rear-facing restraint can also occur during a severe rear impact or offset rear impact, which can result in serious injury or death if the infant's head hits the rear door pillar of a sedan, the rear window of a pickup, or some other hard surface. As larger and heavier infants are carried rear-facing, the chance of an infant's head hitting a hard part of the vehicle is greater. Tethering a rear-facing convertible CR to the floor can reduce the risk of head and facial injuries in rear and side crashes by reducing head excursion.

 

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