Technical Encyclopedia

5-point harness

A CR harness that has a webbing strap over each shoulder, one on each side of the pelvis, and one between the legs, with all five coming together at a common buckle. See also Harness types.

5-Step Test

A measure of how fast a body (mass) gains or loses velocity as the result of a force being applied to that body. Deceleration is negative acceleration.

Adjustable upper anchorage (AUA)

A system built into the vehicle that raises or lowers the shoulder belt anchorage to help place and keep the belt crossing the shoulder between the neck and arm. See also Shoulder belt positioner.

Aftermarket accessory

A product designed to be used in conjunction with child restraints or vehicle belts for improving comfort, fit, or installation or for providing solutions to issues of child behavior. Most of these are not covered by federal regulations, but some have been voluntarily tested by their manufacturers under conditions similar to FMVSS 213. If so, the manufacturer should be able to provide test results upon request. However, some test results may be misleading, because available crash dummies are not able to assess abdominal injury potential. See also Belt-shortening clip, Belt tightener, Harness strap cover, Locking clip, Padded inserts, Shoulder belt positioner.

More on this topic: Transport Canada, Third-Party Aftermarket Products for Children’s Restraint Systems. (3/07)

Air bag

Front passenger air bags and rear-facing restraints can be a deadly combination. Air bags are stored in the instrument panel and inflate at a very high velocity, so they can be in place in time to be energy-absorbing cushions for adults moving toward them in a frontal crash. A rear-facing restraint in the front seat places the child’s head very close to the air bag module, and direct impact from the air bag or housing as the bag deploys has caused over 25 infant deaths, most of them in the 1990s. These incidents are much less common now, however, as the public has become educated about the issue. Older children also have been killed or seriously injured by front passenger air bags when they were “out-of-position,” or too close to the air bag when it deployed. These children sustained head or neck injuries, often in minor crashes, because they were unrestrained or improperly restrained and were leaning forward at the time of a crash or moved forward when the driver braked. NHTSA’s recommendation that children sit in the rear seat until they are age 12 (and can then sit in the front) is partly based on the absence of air-bag-related fatalities to children over age 12 in minor crashes. To minimize unintended injuries from air bags, newer vehicles have “depowered” or “smart” air bags. Depowered air bags deploy with less force, which should be less injurious to out-of-position occupants. Smart air bags use sensors so they do not deploy when the occupant is too small or is too close to the air bag. There is an indicator on the vehicle stating when the air bag is deactivated, because a child or other object of similar size and weight (large purse, bag of groceries) is in that seating position. If the indicator light flickers or the signal is otherwise unclear when a child is sitting in the right-front seat, the child should remain in the rear seat, and the vehicle dealer should be notified. Because it is difficult for consumers to tell which kind of air bag they have in their vehicles, and also because the sensor technology is not perfect, it is always best practice to have children sit in the rear seat, especially those in rear-facing restraints. If a child needs to sit in a position with a frontal-impact air bag, the child least likely to be “out-of-position” should be placed there. This means it would be better to have a properly restrained child in a forward-facing child restraint in front of an air bag than a child in a booster seat or safety belt. In addition, the vehicle seat should be pushed as far back on the track as possible. In some vehicles where a rear-facing restraint cannot be installed in a rear seat (such as some pickup trucks), manufacturers have installed on/off switches for passenger air bags, so they can be deactivated when a rear-facing restraint has been installed. Users must be vigilant to turn the air bag “off” when a rear-facing child is placed there and “on” when an adult passenger is seated there. In more recent vehicles without adequate rear seating, “smart” air bags have replaced the on/off switches. There are several different types of side-impact air bags. Some types are mounted in the vehicle seat or vehicle door, while “curtain” air bags are mounted above the side windows and deploy downward. When side-impact air bags were first installed, there were concerns that they could be a source of injury to children, particularly unrestrained or out-of-position children, including those leaning against the door while sleeping. Most vehicle manufacturers evaluate the injury potential (including out-of-position configurations) using voluntary standards, but there is no way to track this testing. At the same time, field data have not shown any cases of serious injury to children from side air bags. Because curtain air bags deploy downward from above the side windows, it would be almost impossible for a child to be out-of-position relative to these types of air bags. In fact, they have the potential to protect child-size occupants in side impacts and rollovers. (6/08)

Anchor point

A location identified in a vehicle where anchorage hardware, usually for a retrofitted top tether anchorage, may be installed.


A strong point and associated hardware in a vehicle to which a vehicle belt or LATCH attachment is secured. See Child restraint anchorage system, LATCH anchor, Lower anchor, Top tether anchor, Upper anchorage.

A strong point and associated hardware in a vehicle to which a vehicle belt or LATCH attachment is secured. See also Child restraint anchorage system, LATCH anchor, Lower anchor, Upper anchorage, Top tether anchorage.

Angle of recline, forward-facing

The most common recommended orientation for a forward-facing CR is the most upright position. Many convertibles and some child seats have two or more choices of seating angle for forward-facing use, and each of these positions must be certified to FMVSS 213. Although the most upright position probably still provides the most effective overall restraint in terms of load distribution to appropriate bony structures, a certified reclined position may be used for a sleeping child or to make the CR match the angle of the vehicle seat for a tighter installation. It is a good idea, however, to try the most upright position first, because the upright geometry of the CR coupled with the angle of the vehicle seat cushion may sufficiently recline the child to be comfortable. For children seated directly on the vehicle seat, in a backless booster, or in a booster with adjustable back, the normal seatback angle is about 20° to 30° from vertical. This comfort-angle range also applies to adults. If the seatback is tipped farther back than this, there is a danger of the occupant sliding under the safety belt, called submarining, during a crash. This is not a problem in a forward-facing CR, because the entire shell is reclined, not just the seatback, which reduces the likelihood of submarining. Submarining in a CR is also limited by the crotch strap holding the lap straps down on the thighs. Potential injury from spinal loading, predicted in the early days of CR design, has not been shown to be a problem in actual crashes. One laboratory study in England found that a forward-facing CR had to be tipped more than 50° from vertical to generate harmful loading to the dummy, and this is more reclined than acceptable for forward- or rear-facing CR use. (9/07)

Angle of recline, rear-facing

The back surface of a rear-facing CR should be between 30° and 45° from vertical, starting with the most reclined angle for a newborn and becoming more upright as the baby grows. This recommendation is a balance between crash protection and comfort. If the CR is too upright, the head could flop forward uncomfortably and possibly pinch off the airway, especially for a newborn. If the CR is too reclined during a frontal crash, the infant could slide toward the top of the restraint, exposing the head to injury, especially for the larger, heavier baby.

Each manufacturer determines an optimum back angle for its products and specifies a way, such as a level indicator, for the user to determine that angle. However, these indicators only work when the vehicle is level, so they can sometimes be misleading. The Federal standard allows the back of a rear-facing CR to rotate downward as much as 70° from vertical during the FMVSS 213 crash test, but this extreme result reflects the test conditions and would not represent good crash performance. To meet these test requirements, some restraint manufacturers may install their position indicators so the initial angle is too upright for a small infant. For these situations, installing the seat with the indicator outside the specified zone may be necessary, or one must obtain a different safety seat. The baby’s airway must not be compromised.

To set an appropriate back angle for the child, install the CR in the car and put the baby in the CR with the buttocks in the deepest part of the CR and the baby’s back straight. Jostle the CR a bit, and, if the baby’s head flops forward (while awake or asleep), it is necessary to increase the angle. For infant-only restraints, some bases can be adjusted if more recline is needed, or a detachable base can be removed and the shell alone reclined a little more. Otherwise, for these and for convertibles, insert a tightly rolled towel or sheet or a foam “noodle” under the toe-end of the CR to compensate for the slope of the vehicle seat. Increase the angle of recline just enough to keep the baby’s head from flopping forward, but no more than 45° from vertical.

The American Academy of Pediatrics currently recommends that infants born at less than 37 weeks gestation be monitored in a semi-upright position prior to discharge to detect possible breathing, oxygenation level, and/or heart rhythm problems (AAP, 2009). If a baby needs to be more reclined than 45°, he must be tested similarly in a car bed to see if discharge is appropriate, and if so the car bed must be used for travel. There is also evidence that prolonged (over an hour) semi-upright positioning may lead to reduced oxygen saturation levels even among term infants. It is therefore recommended that very young infants not be left undisturbed in their rear-facing child restraints for long periods.

As the child grows, becomes heavier, and can hold his head erect, the angle can be decreased, making the restraint more upright, to provide better crash protection. For a sleeping baby, this angle should be at least 30° from vertical. In addition to improved comfort, keeping the back of the baby’s head in contact with the CR provides better protection in a crash. In some vehicles, the back seat may be too small to accommodate a convertible CR that is reclined as far as 45° in the rear-facing position. For older babies, the CR may be used at a more upright angle to make it fit in the car, but a newborn may require a smaller infant-only restraint. (9/07)

Automatic locking retractor (ALR)

A vehicle belt retractor that allows the belt to be pulled out initially but locks when the pull-out action stops and tension is again applied. The retractor keeps the belt from being pulled out farther until it is fully retracted again. These systems tend to tighten progressively while in use and can be found on older lap belts. See also Emergency-locking retractor, Switchable retractor.

Back angle
Backless booster
Backless child restraint

A type of booster, as defined by FMVSS 213, intended to distribute the loading of a lap belt over a wider area of the child’s body. It is required to be crash tested using only a lap belt and using the head excursion limit of 32 inches. Currently, no boosters of this type are sold in the U.S. Originally, all restraints of this type were shield boosters, which have a seating platform and a structure in front of the child for restraint. Shield boosters are no longer considered appropriate child restraints, because harnessed child restraints offer better protection for the sizes of children who can use shield boosters (under 40 lb). The Britax Laptop (now discontinued) did not have a boosting platform but had a similar-looking shield and was rated for children from 30 to 65 lb. The Laptop still considered a better choice than a lap belt only for children over 40 lb when shoulder belts are not available in the rear seat. (9/06)

Belt-positioning booster (BPB)

A firm seating platform used with a lap-shoulder belt that raises the child relative to the safety belt system to improve lap-shoulder belt fit. Booster seats improve belt fit and crash protection in several ways. First, the booster seat raises the child so the height of the tops of the thighs and the shoulders are closer to those of an adult, for whom the belt system was designed. Second, raising the child changes the angle of the lap belt to be more vertical, which promotes loading of the lap belt on the pelvis rather than the abdomen. Third, the booster cushions are shallower than vehicle seat cushions, so a child’s knees can bend comfortably at the edge. This encourages a child to sit up straight with his back against the seatback, which also improves belt fit. Fourth, booster seats usually have guides or handles near the hips, which position the lap belt and lower part of the shoulder belt. These guides hold the lap belt low and flat across the child’s upper thighs, while the same guide on the buckle side also pulls the shoulder belt toward the child, makes the belt angle more vertical, and helps position the shoulder belt across the center of the child’s chest and between the neck and arm. Never use a pillow or cushion as a booster seat for a child or an adult. In a crash, it can be compressed or slide out from under the occupant, resulting in a very loose belt. Other seats sold as chairs for children or to boost a child in an adult chair should not be used as booster seats in a vehicle, because they would not be able to route the belt correctly. There are three types of BPBs: (A) backless boosters, (B) highback boosters (see also combination seats), and (C) removable-back boosters. Backless boosters can be used on any vehicle seat that supports the child’s head to the top of the ears. These have the advantage of allowing the child to sit farther back in the seat, reducing head excursion, and to take advantage of the vehicle seatback’s comfortable padding, contours, and back angle. Using a backless booster, which is not easily visible from outside the vehicle, may also be preferable for an older child who is reluctant to continue using a booster. Some backless boosters also have a shoulder belt guide on a strap attached to the base to allow adjustment of the shoulder belt position. Use of the shoulder belt guide is optional if the shoulder belt fits the child well without it. Highback boosters are constructed with the base and seatback as a single unit and are often packaged as a combination seat. A removable-back booster consists of a base and seatback that can be used together, or the base can be used alone. A booster with a back is needed in vehicles with low seatbacks and no headrests to allow restraint of the child’s head in a rear impact. However, a few booster backrests must be supported by the vehicle seatback or headrest, so it is important to check the instructions carefully. Some highback and removable-back boosters have side impact protection features and/or lateral support features that can keep a sleeping child in position relative to the safety belt. Both types B and C have shoulder belt guides or clips to help route the upper end of the shoulder belt. For designs with the clip, it is not necessary to route the shoulder belt through the clip if the shoulder belt fits well without it. Highback boosters are supposed to be limited in weight by FMVSS 213 to 4.4 kg (9.7 lb), to keep heavy boosters from loading the child from behind. However, NHTSA is not consistently enforcing this weight limit. For any type of booster, the shoulder belt should be positioned about halfway between the neck and arm, not at the edge of the shoulder or rubbing on the neck. As long as the belt is snug, neck injury is not a prevalent problem, even if the belt touches the side of the neck, but it can be uncomfortable and may lead the child to put the belt under the arm or behind the back, which is very dangerous. Less mature or very active children may need some help staying correctly positioned for the entire trip. This might be encouraged by preventing the shoulder belt from loosening, either by locking the shoulder belt with its switchable retractor (if available) or by using a highback booster with a shoulder belt guide that does not allow the child to pull out the webbing. Be careful with some belt guides that may allow the child to lean forward and/or pull the belt out but have enough friction to keep it from automatically retracting again, as loose belts can result in injuries. It is not recommended that a locking clip be used to keep an active child in position on a BPB or to keep an unstable BPB in place. In a collision, the child’s upper body bends forward, loading the shoulder belt, which pulls the lap belt tight to prevent submarining. Using a locking clip to hold the two parts of the belt together could hold unwanted slack in the lap belt or prevent the lap belt from tightening as it should. Because booster seats are positioning devices and not usually attached to the vehicle, they may shift around when children are entering or exiting the vehicle or sometimes during vehicle travel. Caregivers have asked, particularly with combination seats used as boosters, whether boosters can be attached to the vehicle with the top tether or lower attachments to prevent the shifting. Instructions for some boosters currently being sold allow them to be attached to the vehicle, so users should check their instructions to see if this is permitted. Ideally, children should continue to use a CR with an internal harness until they have exceeded the height and/or weight limits. BPBs are the next step, but only for seating positions with lap-shoulder belts; they should not be used with lap belts alone. This is due to a number of factors. The head of a child sitting on a booster is higher and, with a highback booster, farther forward than the head of a child sitting directly on a vehicle seat. In addition, a lap belt going over both the child and the booster will be longer than a belt going over the child only. Without a shoulder belt to hold the upper torso back, the higher, more forward head position by itself increases the risk of head contact, but the added lap-belt length will allow even greater head excursion in a crash for a child on a booster than for a child on the vehicle seat. Children should continue to use a BPB until both the lap-shoulder belt and vehicle seat cushion fit properly. The age at which a child “fits” the adult restraint will vary with the child and the vehicle. For example, short and heavy children tend to need boosters longer than tall and thin ones, but thin ones may not have sufficient pelvic girth for the lap belt to lie correctly. Since there are many combinations of child sizes, seat depths, and belt geometry, the only sure way to determine the need for a booster is to buckle the child into the belt and apply the 5-Step Test. (9/06)

Belt-shortening clip

Metal hardware used to fix the length of a lap belt with an emergency-locking retractor (ELR). It is sometimes called a “heavy-duty” locking clip. It should be used with either a lap-only belt having an ELR or with an ELR lap belt sewn separately to the lap-shoulder-belt latchplate. These types of belts are generally found only in pre-1996 vehicles. The CR is installed with the lap belt, then the excess belt webbing is pulled out, and the belt-shortening clip is used to lock a loop of webbing, so that the remaining length permits a tight installation of the CR. It is important not to use a regular locking clip, supplied with the CR, when a belt-shortening clip is needed. They have the same shape, but the belt-shortening clip is usually thicker or made of stronger material. Some vehicle owner’s manuals instruct parents on the use of a locking clip to shorten a belt without providing the information they need to distinguish between a regular locking clip and a belt-shortening clip. A belt-shortening clip can be used to do the job of a regular locking clip, but not vice versa. Some of the clips have codes (numbers and letters) stamped into the metal, but these codes do not correspond with the part number on the package. Some of the clips have no identifying information stamped on them at all, and one (no longer made) had the misleading stamp “heavy duty.” The only way to identify a belt-shortening clip positively is to obtain the clip in the original packaging. Instructions must be followed carefully. If the packaging does not include instructions for belt-shortening, check the vehicle owner’s manual. Use the part number below to order the clip from the dealer parts department. (9/07)

  • Ford – F03Z-5461248-A
  • Toyota – 73119-22010
  • Nissan – H8010-89970
Belt tightener

An aftermarket device to wind up excess webbing and lock it in place. These products are not regulated by FMVSS 213, although manufacturers have advertised testing their products using similar procedures. When used to take up slack that could not otherwise have been eliminated by the installer, they may provide a valuable function. Current product designs and instructions, however, may require that more webbing be wound around the device than would be needed to augment normal tightening.

Built-in child restraint system

A CR that is an integral part of a vehicle seat. These are tested according to FMVSS 213 with similar requirements as add-on CRs. The primary difference is the crash test “pulse,” which may be more or less severe than the standard pulse, depending on the particular vehicle in which the CR will be included. Built-in restraints have the potential advantage of linking the child more directly to the vehicle (see Ride-down) and eliminating installation errors, but the disadvantage is that they cannot be moved. Some vehicle seats with built-ins are also found to be uncomfortable when used by adults. Current built-ins take the form of child seats, combination seats, and belt-positioning boosters. There are no built-in rear-facing restraints in production in the U.S. (9/06)

Button on lap-shoulder belt webbing

Federal regulations require that the safety belt latchplate be in a position where it can be reached easily by the occupant. Some vehicle manufacturers keep the latchplate in this position by placing a plastic button on the lap-shoulder belt webbing that keeps the latchplate from falling down out of reach. In some cases, the button prevents the belt from moving through the latchplate far enough to allow secure installation of a CR. If this is the case, the button can be pried off, taking care not to cut the belt. (6/08)

Car bed

An infant restraint that allows the baby to lie flat, with the primary restraint surface being the side of the bed. This type of restraint should only be used by infants who can be discharged but may have medical problems that are aggravated by sitting semi-upright in a regular rear-facing infant restraint. The American Academy of Pediatrics recommends that infants born at less than 37 weeks gestation be monitored in a semi-upright position prior to discharge to detect possible breathing, oxygenation level, and/or heart rhythm problems (AAP, 2009). This is called angle tolerance testing. The test should last one hour or the length of the ride home, whichever is longer. If the infant does not pass the test, she should be retested in a car bed to determine if discharge is appropriate. If so, the infant can be restrained for travel in a car bed, which is sometimes available for loan or purchase through the hospital.

In a car bed, the infant lies flat, preferably on his back, with a harness or bunting to hold the infant in position. The car bed is placed across the vehicle seat in the center position, or with the baby’s head toward the center of the vehicle (not towards the door) in an outboard seating position. During a frontal crash, the front side of the car bed distributes forces over the side of the infant’s body, with the harness providing restraint during rebound or rollover. For side impact, the infant would theoretically be safer in a standard rear-facing CR, especially if there is significant intrusion on the side of the vehicle closest to the infant’s head. There are not enough car beds used to document statistically the effectiveness of this type of restraint, although field experience has not demonstrated any widespread problems.

There are three car bed models available in the U.S., which accommodate infants from very low birth weight to an average 1-year-old. It is recommended that car beds be installed in the rear seat with an adult sitting next to it to monitor the infant, since the rear seat is less dangerous for all children and there is a potential for excessive loading by the air bag in the front seat. (9/07)

Carry handle

A semi-circular loop of hard plastic that is attached to each side of an infant-only restraint and can be rotated to various positions. It is used to carry the CR outside of the vehicle. Carry handles are only for carrying and do not lock the shell into the base. One product, no longer manufactured, used a carry handle made of fabric. During vehicle travel, the handle must be locked into one of the designated positions, which may be described as follows: ‘up’ is in the carrying position, ‘back’ is behind the head, and ‘down’ is the lowest position, pointed toward the floor. A fourth position, braced against the seatback, is not common here but is used in Europe and Australia to restrict rebound. Most manufacturers recommend locking the carry handle in the ‘back’ or ‘down’ position, although some allow and may even require the handles to remain ‘up’ during travel. Many handles are now being tested for use in the ‘up’ position and as anti-rebound devices. It is therefore necessary to read and follow the handle instructions for the specific CR used. There have been some rare cases of injury from head contact with the handle. In these cases, the handle broke, and a child in a loose harness moved close enough to contact the damaged handle. In another case, a side curtain air bag broke the upright handle and allowed it to contact the child, causing minor injuries. Other injuries have occurred when the parents used the CR as a carrier outside the car, the handle rotated, and the baby slipped out of a loose or unused harness and fell to the ground. Several manufacturers of infant restraints have had recalls by the U.S. Consumer Product Safety Commission for handle breakage problems, so handle locking designs are now more reliable. However, parents should avoid swinging infants in a CR by the handle and always make sure the harness is secured and snug. (9/07)

Child restraint anchorage system

A standardized system of user-ready hardware in vehicles, consisting of two lower anchorages and one upper anchorage specified in FMVSS 225, for installing child restraint systems independent of the vehicle seat belt; popularly referred to as LATCH in the U.S. and similar to the Canadian Lower Universal Anchorage System (LUAS).

Child restraint fixture (CRF)

A physical model representing the outside dimensions of a combined rear-facing and forward-facing child restraint (see FMVSS 225, figures 1 and 2) that is used by a vehicle manufacturer to determine the space required by child restraint systems in a given seating position and the location and accessibility of the lower anchorages in that position.

Child restraint system

A general term used in FMVSS 213 for devices designed “to restrain, seat, or position children who weigh 65 pounds of less.” These include rear-facing restraints (infant-only and convertible), forward-facing restraints (convertible, child seat, combination seat), car beds, harnesses, and boosters (belt-positioning and shield). Any of these could also be designed and produced as built-in CRs, but currently only forward-facing systems exist. The standard specifically excludes vehicle belts (lap or lap-shoulder) from its definition. Common alternative terms are “child safety seat” and “car seat.” The latter term should be avoided because of its likely confusion with “vehicle seat.” (1/07)

Child seat

A common term for a CR that only faces forward and has an internal harness. All current models have a 5-point harness system. Most of the products of this type restrain children up to 40 lb with the harness and can then be used as a belt-positioning booster when the harness is removed (see also Combination seats). Some of these products are now designed to restrain children up to 80 lb with a harness, although they cannot be converted to a booster seat. For these higher-weight, harness-equipped seats, some require use of a top tether if the child weighs more than 50 lb. The minimum weight for a child using these CRs varies from 20 to 30 lb. The advantage of this type of CR is that the harness slots are usually higher and the back usually taller than a convertible CR used forward facing, so they may better accommodate taller children under 40 lb who outgrow their convertible CR because of height. A disadvantage compared to convertibles is that they are typically more upright and have shallower side supports, which may be less comfortable for the child, particularly on longer trips. Some child seats can be reclined slightly, which can improve comfort as well as fit with the vehicle seat. (1/07)

Cinching latchplate

Many CR covers are machine washable, while others can only be spot cleaned. Refer to the instructions. Buckles can be washed with mild soap and water and air-dried, but lubricants should not be applied to buckles. Harnesses can be washed, but soaking may leave the webbing stiffer than before, and bleach can weaken the material. It is sometimes not possible to completely remove the harness from the CR, so spot cleaning may be necessary. Do not remove webbing from latching or adjustment mechanisms unless there is a detailed threading diagram in the instruction booklet. Harness ends that are folded and sewn are not intended to be removed. For fabric covers, carefully follow the washing instructions provided by the manufacturer to retain fire retardancy.

Cocoon effect
Cold weather

During cold weather, what is the best way to keep my child warm in his safety seat? Clothing worn by children can present compression and harness routing problems. Bulky jackets and snowsuits can compress in a crash and leave the harness slack on a child, allowing excessive movement or even ejection. It is best to have children travel with their coats worn backwards after harnessing, or to add a blanket over the child after the harness has been buckled. If you are planning to harness your child in a jacket, the jacket should be no heavier than lightweight fleece fabric or be unfastened to allow contact between the child and the harness or vehicle belt. A useful test to see if a jacket is too bulky is to buckle the child into the harness with the coat on and adjust the harness to a snug fit (do the pinch test), then unbuckle the harness, remove the coat and re-buckle. If slack has been introduced to the harness, the jacket is too bulky. An option for a child in a rear-facing-only seat is a shower cap-style seat cover. This style of cover fits over the top of the seat, has an elastic band around the edge, and has no fabric behind or under the child. For more on this topic, go to Padded inserts, blankets, and bulky clothing.

Combination seat

A forward-facing CR that has a removable harness and can also be used as a belt-positioning booster (see that entry for a drawing as a booster). For most products, this transition is made when the child reaches 40 lbs. Other common names are “child seat/booster,” “CR/booster,” “child seat/BPB,” or simply “combo.” To prevent confusion, they should not be called convertible seats, which has another meaning, or highback boosters, since that only describes half of its function. Several manufacturers make two models with the same plastic shell: a combination seat with a removable harness and a BPB sold without the harness. The advantages of purchasing a combination seat while the child is still under 40 lb are the higher back for head support and possibly higher upper strap slots (as much as two extra inches for some) compared to most convertibles, and the ability to convert it to a booster for use beyond 40 lb. A common error with these seats is that caregivers continue to restrain the child with the harness beyond 40 lb instead of switching it to booster mode. Manufacturers prohibit use of the internal harness and the lap-shoulder belt over both child and shell because of possible interaction between the lap belt and the harness buckle and between the shoulder belt and the harness retainer clip. Combination seats come with top tethers for use in the child seat mode, and this tether should definitely be attached as the child approaches the maximum harness weight. Keeping the tether attached for the booster mode is not likely to affect crash performance, but it may be useful to stabilize the booster as the child climbs in and out, during vehicle turns, and to keep the tether hook contained. Check the manufacturer’s instructions, which may advise removing the tether when the product is used as a BPB. Nearly all manufacturers state that LATCH lower attachments are not to be used in the BPB mode (check instructions for exceptions). Some say to stow them on the CR, while others say to remove the hardware and store it with the harness. These pieces must be replaced when the product is again used as a child seat. For more information on the use of lower attachments in the booster mode, see LATCH. (9/06)


Hardware at the end of a LATCH attachment, such as a top tether hook specified in FMVSS 213 or other latching device compatible with lower anchorages specified in FMVSS 225, that enables the CR to be securely fastened to a LATCH anchorage. Lower connectors can be either a hook-on type or a push-on type, where a spring-loaded latch automatically locks around the LATCH anchor bar.

Convertible child restraint

A CR that can be used rear-facing for infants up to at least 22 lb or as much as 35 lb, and then turned to face forward until the child reaches the product’s upper weight limit, usually 40 lb. Most current convertibles can accommodate children rear-facing up to 30 lb.

Date of manufacture

The date that the product was completed at the factory. This date must be printed on the product itself, and the CR must meet all Federal requirements in effect on that date. A CR may be sold any time after the date of manufacture but does not have to meet any new requirements that become effective in the meantime. The date of manufacture is needed (1) to determine if the CR should be replaced because it is too old, (2) to determine if the CR is on recall, and (3) to order the correct top tether anchorage kit, if applicable. If the parent purchased the CR new and knows its approximate age, and there are no recalls in effect for that particular model, it is not essential to know the exact date. There is no agreement on “how old is too old.” At one time it was important to check that a CR was made after 1980, because 1981 was the year the Federal regulation requiring crash testing went into effect. Today, however, 1981 is not an appropriate point of reference for brochures and teaching materials, since CRs made that long ago should not be used anyway. Several years ago, Transport Canada issued a very reasonable statement, which others have adopted, that basically said that, after about 10 years, a CR is not likely to have all its parts and instructions nor have the important warnings and convenience features found on later models. There may also be some deterioration from heat and sunlight, but the validity of this concern has not been documented. See also Expiration date.


Anthropomorphic (shaped like a human) test device specified in Federal standards, such as FMVSS 208 and FMVSS 213, to measure the protective capabilities of restraint systems in simulated crashes. The child restraint standard includes four dummies: Newborn (7.5 lb), P-¾ 9-Month (20 lb), VIP 3-Year (33.5 lb), and Hybrid II 6-year (47 lb). The air bag standard uses a different set of newer dummies: CRABI 12-Month (22 lb), Hybrid-III 3-Year (34 lb), and Hybrid-III 6-Year (51.5 lb). The most recently developed dummy is the Hybrid III 10-Year, which is expected to be used to test boosters and other products for older children. All dummies except the Newborn and 9-Month are instrumented, i.e., equipped to measure various accelerations and forces during testing. For complete descriptions and specifications of each, see the FTSS product catalog.

Dynamic Locking Latchplate

Similar in appearance, but not function, to a locking latchplate, a dynamic locking latchplate locks the lap portion of the safety belt only during a crash, and thus cannot be used to secure a child restraint. If installing a child restraint in a seating position with a dynamic locking latchplate, the retractor must be locked.

Emergency-locking retractor (ELR)

A vehicle belt retractor that locks when the vehicle stops suddenly, including sudden braking. It is activated when there is sufficient vehicle deceleration to allow a freely moving pendulum or, more recently, a ball-in-cup mechanism to engage and lock the retractor. Current vehicle retractors have an additional back-up feature that locks when the belt webbing is rapidly pulled out. After the tension is released, the belt can again be pulled out gradually. See also Switchable retractor.

Energy absorption

The transfer of crash energy to the permanent deformation of mechanical structures. This deformation can involve vehicle sheetmetal, padding that does not bounce back (such as expanded polystyrene), or an air bag undergoing controlled deflation. See also Ride-down.

Energy management loop (EML)
Expiration date

In the last few years, CR manufacturers have been putting “expiration dates” on their products. This was begun in response to infant deaths from air bags. The companies realized that they had millions of products in use that said nothing about the danger to a rear-facing child. The concern became one that “best practice” and regulations change over time, so that a child restraint becomes “obsolete” and less effective than a new product, much the same way that medicines may change or become less effective after some time has passed. A current example would be with tethers–older CRs do not have them, and this is potentially a situation where a newer product will be more effective than an older one. Taken at face value, the expiration interval (ranging from 5 to 8 years, depending on the manufacturer) is from the date of manufacture, which is what governs the labeling, certification, and other rules that apply. Whether to continue to use an “expired” CR is a judgment call, depending on the alternatives. It will work as well as before, but it is important to know what regulations and warnings may have changed and the risks involved. It is also important to take the expiration date into account when purchasing a CR that may have been manufactured several months or even a year or more before.


The U.S. Federal Motor Vehicle Safety Standard that establishes requirements for the protection of vehicle occupants in crashes by specifying limits on forces and accelerations measured on anthropomorphic dummies in test crashes, and by specifying equipment requirements for active (vehicle belt) and passive (air bag) restraint systems. See a complete copy of FMVSS 208 (PDF).


The U.S. Federal Motor Vehicle Safety Standard that establishes requirements for child restraint systems designed for use by children up to 50 lb in both highway vehicles and aircraft. These requirements cover crash performance, geometry, instructions and labeling, durability, flammability, and product registration. See a complete copy of FMVSS 213 (PDF). See also Date of manufacture, HIC, Head excursion, Height and weight limits, Instructions, Labels, Padding.


The U.S. Federal Motor Vehicle Safety Standard that establishes requirements for child restraint anchorage systems, also known at LATCH, in highway vehicles. These requirements cover the location and strength of the anchorages for effectively securing child restraints. See a complete copy of FMVSS 225 (PDF).

Forward-facing child restraint

A restraint that is installed so that the child faces the front of the vehicle. Current models may be a convertible, child seat, combination seat, backless child restraint, shield booster, or belt-positioning booster. See also Rear-facing vs. forward-facing.

Front seat use
Funnel guide

A device incorporated with some lower anchorages to help the user position and guide the lower attachment connector during CR installation.


The webbing assembly attached to a CR shell or frame that restrains the child in a crash. It is equipped with a buckle, a method to adjust it snugly against the child, and usually a harness retainer clip. See also Harness types. The term is also used to describe independent restraint systems made from webbing, connectors, and adjusters, but without a shell, that are often referred to as “child harnesses”. These products are typically recommended for situations where a standard CRS cannot be used, such as on school buses, when transporting older special needs children who need more torso support than provided by a three-point safety belt, and in lap-belt only seating positions where a CRS with higher weight limits cannot be used. Some harnesses attach to the vehicle with only a lap or lap-shoulder belt, while some also require use of a top tether strap. If used for a child over 48 lbs, standard tether anchorages installed in vehicles may have to be replaced with a stronger anchorage. Child harnesses are tested according to FMVSS 213 to meet the head excursion limit of 32 inches and the injury criteria for the head and chest. Their use is prohibited on aircraft. (3/07)

Harness retainer clip

A plastic device that holds the shoulder straps of a harness in place on the child’s chest to achieve good pre-crash positioning. During a crash, the clip often is designed to either slide down the straps or separate if it has two parts. The harness clip should be placed at the level of the child’s armpits. For small babies, if there is not enough room above the buckle to position the clip at the armpits, a different CR should be used. The purpose of the clip is not to hold the child in the restraint, but to keep the shoulder straps in position, which is especially important if the harness is not adjusted snugly.

Harness slot selection

For a rear-facing CR, use harness slots that are at or below the child’s shoulder level. In a frontal crash, the shoulder straps routed below shoulder level prevent the child from “ramping” or sliding up above the top of the CR, possibly resulting in head or neck injury for a larger child. If the lowest slots are above the infant’s shoulders in a convertible, try an infant-only restraint instead. For newborns, choose a restraint with at least three sets of slots, so the bottom slots are very low. If the lowest available slots are still above the shoulders, make sure the harness retainer clip holds the shoulder straps over the chest. Because of the child’s short body and light weight, the risk of excessive ramping in this case is minimal.

For a forward-facing CR, harnesses should be routed through slots that are at or just above the child’s shoulders, which allows the child’s shoulders to immediately load the belt. For convertible CRs, caregivers need to check the instructions to determine which harness slots can be used forward-facing. On older convertibles, only the top slots could be used in forward-facing mode, because the lower slots were not reinforced to adequately restrain a forward-facing child in a frontal crash. If a harness is routed through slots that are not designed for forward-facing use, the shell may break out or the straps rip through the plastic, allowing excessive head excursion or even ejection. (3/07)

Harness strap cover

A padded fabric sleeve that covers harness straps at the shoulders. It is intended to prevent the edge of the shoulder strap from rubbing against the child’s neck. Some harness strap covers come with new CRs, while some are sold as accessories and may be longer than necessary. If they prevent the harness retainer clip from being properly positioned at the armpit, the covers should be removed or shortened. The fabric harness covers that come with a CR do not need to be used if the child does not like them. However, at least one CR manufacturer uses rubber sleeves over the harness straps to improve interaction between the harness and child. These cannot be shortened and should be used and positioned according to the manufacturer’s instructions. (3/07)

Harness tightness

A snug but comfortable harness is important for good crash protection, because the more tightly that occupants are belted, the more they can take advantage of “ride-down” with the vehicle. If there is a lot of slack in the harness at the time of a crash, the child first moves forward unrestrained but is then abruptly stopped by the loose straps. This can cause greater injury than if the straps were already snugly against the child’s body. NHTSA now requires that child restraint manufacturers include the following description in their instructions: “A snug strap should not allow any slack. It lies in a relatively straight line without sagging. It does not press on the child’s flesh or push the child’s body into an unnatural position.” A common way to check that the harness is snug enough is the pinch test. After adjusting the harness so it is comfortable, try to pinch the harness webbing along its length (not its width). If you can grab some of the webbing, it is too loose. Some older guidelines state that there should be enough slack in the harness to insert one or two fingers between the webbing and child, but this measure is not as good because children’s bodies are soft and pliable. When testing a 5-point harness (see Harness types), pull all of the slack from the lap part up into the shoulder straps before checking for tightness. If the harness does not touch the baby’s body even when it is pulled as tight as possible, the problem cannot be solved for this model of CR. Such a situation can occur with small babies in some infant-only restraints and most convertible CR with shields. For distribution programs, staff should check for this potential problem before selecting the CR models they will provide to the public. Parents who already have such a CR should be encouraged to replace it (if new) or use a different model until the child is bigger. This is particularly important if the model has a shield (see Harness types). If there is a gap between the crotch strap and the infant’s crotch, a rolled diaper or washcloth may be placed in this gap to help prevent slumping. After adjusting the harness, be sure the strap length is locked in place. Many CRs have levers in front that automatically clamp the webbing, but tug on the straps to be sure. For rear-facing, be sure the lever is not caught in the “up” position against the vehicle seat. Also check that the connector hardware or stitched webbing in the back is not caught somewhere, leaving hidden slack. Some older CRs use a system where one end is sewn to a metal slide and the other end is free. Before adjusting the harness, the free end is threaded through the metal slide sewn to the other strap end. At this point, it looks like a buckle on a shoe. After adjusting the harness to the correct length, the free end of the strap must be looped back through the metal slide one more time to lock the webbing in place. When properly secured, the metal slide should look like a “C” (for correct), not like an “O” (for open). Another design has one end of the harness strap sewn to a metal slide, which must lie flat against the plastic on the back of the CR shell, in a location designated by the CR manufacturer. A common misuse is to have the end with the slide dangling, which introduces hidden slack. Vehicle belts on children in belt-positioning boosters also need to be snug, but again not uncomfortably tight. The tension provided by the retractor may be adequate to keep the belt snug, but it is designed to allow some movement of passengers during travel. It may be necessary to lock a switchable retractor, if the shoulder belt does not stay properly positioned on a wiggling or sleeping child. Make sure the shoulder-belt guide attached to the booster does not grip the belt, preventing it from retracting after the child leans forward. (3/07)

Harness types

All CRs have a harness, a shield, or a combined harness/shield to directly restrain the child’s body. There are several harness types. Safety experts recommend selection of CRs with 5-point harnesses unless circumstances require use of another type.
The 5-point harness (A) has a strap over each shoulder, one on each side of the pelvis, and one between the legs. All five come together at a common buckle. The function of the crotch strap is to hold the lap straps firmly down on top of the thighs, and it should be as short as possible. Because the crotch strap is merely a lap-strap positioning device, the actual restraint should come from the shoulder and lap straps. This type of harness fits children best, since the straps can be adjusted closely around the child’s body, and the straps direct the crash forces at the child’s strongest bony structures, the shoulders and pelvis.

The harness with tray shield (B), also called an “overhead shield,” has shoulder straps attached to a curved plastic bolster, which is in turn attached with pivot arms to the sides of the CR shell and held down by a crotch strap and buckle. The tray shield was designed to take the place of the lap straps while being easier to use. Some harnesses can be removed from the shield for cleaning, but it is essential to re-connect the harness for the systems to work properly. Many parents perceive that the shield is more protective than straps, but this is not the case. In reality, the opposite may be true. This harness/shield system is not suitable for small babies, since it cannot be made to fit a small body tightly, and the shield may interact with a small child’s neck or face. Some tray shields are adjustable, which improves fit somewhat. Tray-shield harnesses should only be used when the caregiver is unable to correctly use a 5-point harness system (e.g. arthritis in hands or other disability).

The harness with T-shield (C) has shoulder straps attached to a flat, plastic pad on a fairly rigid stalk that buckles into the shell between the child’s legs. There are currently no products being sold in the U.S. that use this type of harness. This system does not fit babies well because the T-shield is not close enough to the child’s body and is positioned on the chest or abdomen instead of the hips. For larger children, the bottom edge of the T-shield can uncomfortably press into their thighs.

Safety experts have concerns about CRs with shields. Tray shields are not usually covered with energy-absorbing padding to protect the head if it hits the shield. This contact is more likely with a shorter child and a loose harness. In a test series with a 12-month-size dummy, peak head acceleration was 35% higher for tray shield restraints than for 5-point harnesses. At least one child (19 lbs) is known to have received a fatal head injury from contact with a tray shield. For T-shields, there is a concern that the throat of a small child may be injured from contact with the top of the shield during a crash. In the same series of crash tests, neck forces were 40% higher for T-shields than for 5-point harnesses, and the crotch load with T-shields was 2.7 times higher than with 5-points. See Weber 2000.

Most CRs currently sold in the US are equipped with 5-point harnesses, although some convertible restraints are equipped with a tray shield. In the past, infant-only restraints have had a “V-harness” or “Y-harness” where shoulder straps come together at a buckle in the shell or on a crotch strap. One infant-only safety seat even had a tray shield. (3/07)

Head excursion

The distance that the head of a child or crash dummy moves in the direction of impact or on rebound from a crash. Higher head excursions are associated with higher risk of head contact and injury. There are two head excursion limits for forward-facing dummies in FMVSS 213 testing. Before September 1999, the limit was 32 inches forward of a point located about 5 inches rearward of the seat bight. Since that date, nearly all forward-facing CRs have to meet an additional limit of about 28 inches (720 mm) from that point, but they can use a tether to do it. Retaining the old limit provides a guarantee that the CR is structurally sound and will perform as well as older models, even if the tether is not used.

Head Injury Criterion (HIC)

A calculated value indicating the likelihood of serious head injury, which may or may not involve direct head impact. HIC is computed using a complex formula related to the magnitude and duration of dummy head acceleration. Three of the child dummies (12-month, 3-year, and 6-year) used in FMVSS 213 tests measure head acceleration and can be used to calculate HIC. The maximum allowable HIC in FMVSS 213 is a value of 1000 and is based on adult injury tolerances. Many researchers believe the limit should be lower for child-size dummies, as they are when used in FMVSS 208 to evaluate potential air bag injury. (4/07)

Heavy-duty locking clip
Height and weight limits

Manufacturers are required to label each CR with the child weight and height ranges for which the restraint was designed. This labeling determines the dummy sizes used to certify the CR. If a CR is certified for 22 lbs or less, it must be tested with the Newborn and 9-Month size dummies. Certification to 40 lbs requires additional testing with the 3-Year size, and over 40 lbs requires the 6-Year dummy. Most CRs are certified with at least 2 dummy sizes, but those labeled only for children under 11 lbs (a small car bed) or over 40 lbs can be certified with a single dummy. When applying these labeled limits to a child, the maximum weight and the head position are more important than the standing height (or length) in determining when to move to a larger restraint. Children should be weighed from time to time to anticipate when they are approaching the weight limit, and the additional weight of clothing is assumed. Tall, thin children will usually outgrow a CR before this weight is reached, but short chubby children may need to switch while they still fit in the harness and shell. For rear-facing, the top of the child’s head should be below the top of the shell, and a margin of at least an inch is recommended, so that the head will be supported and contact with the vehicle minimized during a severe crash. For forward-facing, the top of the child’s ears should be below the top of the shell, to guard against neck injury (whiplash) in a rear impact. In addition, the child’s shoulders should be below the highest strap slots to minimize slack in the harness. The only way to determine these height limits is to put the child in the CR and see if it fits. Note that many combination seats have higher strap slots than convertibles, even though they are both for children up to 40 lbs. Child restraint systems are engineered with a margin of safety, and they are tested under very severe conditions. It is therefore not necessary to move children out of their CR the moment they exceed either the weight specified or the recommended head or shoulder height. The concern is not that the harness or shell will break, but that, at some point beyond the limits, the CR will not provide optimal protection. The same applies to turning a convertible from rear- to forward-facing. However, with so many choices available today, it is a good idea to plan ahead for the next CR or belt system in time to get and install the best product for the child. This may involve installing a top tether anchorage or retrofitting the seat position with a shoulder belt.

Inflatable Safety Belt

The shoulder portion of this safety belt contains an air bag which spreads crash forces over a greater area of the occupant’s body during a crash. Many CR manufacturers do not allow use of inflatable safety belts with their products. Ford, the initial manufacturer, has ceased using this technology as of 2020.

Installation tightness

A tight installation improves the performance of any CR (see Ride-down), but it is not necessary or possible to make the system rigid. Installation should always include (1) compressing the vehicle seat cushion by pushing down on the CR, (2) removing all of the slack from the lap portion of the vehicle belt or the LATCH lower attachments, and (3) testing the lap portion of the vehicle belt to make sure it is “locked” against loosening (see Lockability, Locking clip). When testing the installation tightness, grab the CR close to where the belt or LATCH attachment routes through the CR. If the CR can still be moved from side to side or toward the front of the vehicle more than an inch (see also Lockability test requirements), there may be a mismatch between the shape of the vehicle seat and the CR or between the belt path and the vehicle belt and/or anchorage geometry. For a rear-facing CR, it is acceptable for the top part of the CR to rotate toward the rear of the vehicle or to shift from side to side, as long as the CR is attached securely near the belt path (see also Top tether, rear-facing). For a forward-facing CR installed in a vehicle where the seatback is adjustable, tip the vehicle seatback rearward, install the CR, then bring the seatback forward. This may help provide a better fit between the CR and vehicle seat. If the installation is still loose, a different seating position or CR model may need to be used. For forward-facing CRs, a top tether should be used whenever possible, but this cannot completely make up for looseness of the vehicle belt or LATCH attachment. (9/07)


CR manufacturers are required to provide printed instructions with diagrams for step-by-step installation of their products, positioning the child, and adjusting the system to fit the child. Various statements are also required about the consequences of not heeding the warnings on the labels, the dangers of air bags, the benefits of rear seats, and which vehicle belts to use with boosters. A storage location on the CR is also required. Refer to these instructions to find out minimum and maximum weights for which the CR is certified; how the harness is threaded, adjusted, and secured to the CR; how the angle of recline is adjusted; how to reassemble the CR correctly (after the harness has been cleaned, for example); the correct position of the carry handle; how to order missing parts; and other special characteristics of the CR. CR advocates and technicians must have access to the manufacturers’ instructions when advising parents. Since parents may not keep the instructions with the CR, it is necessary to have a set of all of the manufacturers’ instructions (1981 through current date) on hand at checkup events. These instructions should be followed exactly, unless prevailing “best practice” has superseded the information provided in older instructions (see also Expiration date). An example would be to turn the child to face forward because the feet touch the vehicle seatback (see Rear-facing vs. forward-facing). The instructions in the vehicle owner’s manual take precedence over those of the CR regarding appropriate seating positions and the way the vehicle belts are used. For example, the CR instructions may state that an emergency-locking, lap-only belt cannot be used to install the restraint, but the vehicle manufacturer can provide a belt-shortening clip with instructions for a secure installation.

Integrated CR

A system for the connection of a CR to a vehicle that has two lower anchorages in a vehicle seating position located near the seat bight, corresponding rigid attachments on the CR, and a means to limit the forward rotation of the CR. The system was developed by an international standards committee and is expected to be adopted by European countries. ISOFIX differs from LATCH and LUAS with regard to the child restraint in that only rigid lower attachments are allowed, and for both CRs and vehicles top tethers are not required.


Manufacturers are required to label a CR with the model name or number, the date of manufacture, a statement that it “conforms to all applicable Federal motor vehicle safety standards,” the weight and height limits for the child occupant, and various warnings about proper installation and use. Some of these must be visible when the CR is installed, which can be difficult when space is limited. There will be no label stating that the child restraint “passed” FMVSS 213 or is “approved.” If the identification labels have come off or are illegible, the CR may still be good, but it will be harder to determine its name, how old it is, and if it has been recalled.

Lap belt clip

A piece of plastic to fasten the loose end of a manual (center) lap belt to the main part of the belt. If this clip makes it hard to pull on the tail to tighten the belt, it may be removed.

Lap belts and children over 40 lbs

While using a lap belt is safer than riding unrestrained, there are now many better choices for restraining children over 40 lbs, who have outgrown conventional CRs but do not have access to a lap-shoulder belt in the rear seat to use with a belt-positioning booster. There are now several convertibles, combination seats, and child seats available to accommodate children who weigh up to 80 lb. In addition, there are special needs CRs that fit larger children. These seats are typically among the more expensive CRs, and they are also bigger than other child restraints, which may prevent installation of another CR or booster in an adjacent seating position. There are also several harness and vest alternatives for larger children. For a current list of all these products, see “Booster Seats and Other Products for Children Over 40 Pounds,” bottom of p.1. Using the top tether is especially important with heavier, taller children in these larger restraints. Likewise, belt-positioning boosters should not be used with lap belts alone, because raising the child, together with the absence of an upper torso restraint, increases the likelihood that the child’s head will contact the vehicle interior during a crash. (7/06)


An acronym that stands for “Lower Anchors and Tethers for CHildren” and refers to the child restraint anchorage system specified in FMVSS 225 and corresponding top tethers and lower attachments identified in FMVSS 213. The system includes lower anchorages in the form of rigid bars installed in the vehicle seat bight and flexible (A) or rigid (B) lower attachments on the CR that connect to the bars. LATCH has been phased into the vehicle fleet, but all passenger vehicles made from September 2002 must have the system in a certain number of seating positions. LATCH is also required on child restraints (with a few exceptions) manufactured from September 2002 and is available on many models made before that date. The exceptions include car beds, child harnesses, and belt-positioning boosters.

The LATCH system allows you to securely attach your safety seat in your car without using the vehicle belt and possibly to get a better fit. For seating positions with LATCH anchors, experts recommend trying the LATCH installation first and only using the vehicle belt in that seating position if LATCH, for some reason, results in a looser fit. If you want to use the center rear seat and no LATCH anchors are available (check the vehicle owner’s manual), try the vehicle belt to be sure you can get a tight installation. If you cannot, try the LATCH anchors in a different seating position.

When a combination seat is used in the booster mode, most manufacturers instruct the parent to remove the LATCH attachments from the CR, or at least the lower ones, and store them with the harness. This is primarily due to the weight limitation on highback boosters, which is usually exceeded with the addition of the LATCH hardware. The complication is that the lower attachments are supposed to be “permanently attached,” so other manufacturers instruct that LATCH be detached from the vehicle anchorages and stored on the booster itself, often putting the booster over the weight limit. This aspect of booster regulation and practice is currently in transition. NHTSA has recently said it is not enforcing the 9.7-lb weight limit on boosters that could impose loads from behind and push the child into the belt. Since manufacturers are not required to test booster performance with LATCH, they are reluctant to recommend it, even though such usage would isolate the booster from the child and thus get around the booster weight limit. Expectations for the future, however, are that combination seats and highback boosters will become heavier, a higher weight limit will be established, and other systems such as lock-offs and LATCH will be used with boosters.

For further details, go to our summary of LATCH requirements. For a comprehensive treatment, see SRN’s LATCH Manual.

LATCH anchorage

Hardware in the vehicle to which a top tether or a lower attachment is connected as part of a complete CR installation.

LATCH attachment

A hardware assembly on a CR, possibly including webbing, that connects to a top tether anchorage or a lower anchorage as part of a complete CR installation. See also Connector.


The metal portion of the vehicle belt assembly that connects to the buckle and through which the webbing is threaded. The insertion tip is also called the buckle “tongue.” For lap-shoulder belts, there are “locking” and “free-sliding” latchplates. The locking type will allow the lap portion to be pulled into the shoulder portion but will restrict its slippage back to the lap belt. The free-sliding type allows the belt to slip easily in either direction. A third “cinching” latchplate will hold the belt enough to meet the requirements of the lockability standard but will allow the belt to slip through the slot during a crash. Another variation is the “switchable” latchplate available on a few vehicles. It is normally free-sliding but can be made to lock the belt by moving a dial or button to the “child” position. Lap-only belts also have locking latchplates that restrict slippage once the belt is pulled tight. To hold the locking bar in place and remain tight, however, the webbing must be parallel or nearly parallel (angle of less than 30°) to the latchplate. See also Lockability and Twisted vehicle belt.

Load leg

Extends from the base of the safety seat to the vehicle floor, adding stability and reducing the transfer of crash forces to the child occupant. Found primarily on rear-facing-only seats in the U. S. It is not used in federal crash-testing to the FMVSS 213 standard. However, manufacturers test with and without the load leg in use.

Load limiters
Lock-off device

A clamp attached to the CR that is affixed to the vehicle belt to perform one or more of the following functions: (1) prevent movement of the belt relative to the latchplate, (2) maintain an applied tension on the belt from the floor anchorage through the latchplate to the lock-off, and (3) prevent movement of the CR relative to the belt webbing. If performing function (1), the lock-off replaces a locking clip. If performing function (2), it does not replace a locking clip but eliminates the need for one. It is still useful to lock the switchable retractor, if this feature is available. Function (3) is intended to improve ride-down and pre-crash stability by keeping the CR from sliding relative to the lap portion of the belt, but this lock-off usage does not fix the lap belt length or maintain belt tension. Function (3) does not replace a locking clip or the lockability feature of the vehicle belt.

Lock-offs were first developed in Europe and are defined by European regulations (ECE R44.03 in English, French and Russian) as “a device which locks and prevents movement of one section of the webbing of an adult safety-belt relative to another section of the webbing of the same belt.” Thus they must perform functions (1) and/or (2), largely eliminating the need for locking clips, and some versions also perform function (3), if the lock-off is rigidly attached to the CR.

In the U.S., lock-offs are found on the side or under the center of the shell. To replace a locking clip, both the lap and shoulder portion of the belt must be clamped in the lock-off. When there is a lock-off on each side of a CR, using the far-side lock-off in this manner can be recommended (unlike with a locking clip), because the lock-off is so close to the narrow belt path that little, if any, slack will be released if the lock-off opens in a crash. If only the lap portion is clamped, lock-off use will reduce sliding relative to the belt but will not keep the belt tight. Lock-offs for the shoulder portion only are located high on the side of the shell near the child’s head and should keep the belt tight enough to eliminate the need for a locking clip.

For most CRs, it is acceptable to still lock the vehicle belt with an available switchable retractor in addition to using the lock-off. On some CRs, use of the lock-off(s) is required, but this use is optional for other CRs. An unused lock-off should be left closed and the belt routed over it to minimize breakage. Because use of lock-offs varies with each manufacturer and product, check the instruction manual for proper use of the lock-offs on your CR, even if you are familiar with using them on another product. (9/07)


Starting in the 1996 model year, the lap portion of vehicle belts in all seating positions except the driver’s are required to be “lockable,” so that they “can be used to secure a child restraint system” tightly without any additional device or modification of the belt webbing (FMVSS 208, S7.1.1.5). Most vehicle manufacturers either use locking latchplates or switchable retractors to meet these requirements. The vehicle owner’s manual and labels on the belt webbing describe which feature is provided for lockability. These devices are for pre-crash positioning and do not need to hold the belt in a sudden stop or crash. In those situations, the emergency-locking retractor (ELR) will activate to lock the belt.

With switchable retractors, the normal mode is ELR, where the belt remains at a comfortable tension over the occupant and allows some movement but locks in case of a crash or sudden stop. Because this mode may allow the CR to shift out of position during normal driving, these retractors must be switched into ALR (automatic locking retractor) mode when installing a child restraint. The CR is installed with the belt, then all of the webbing is pulled out of the retractor to switch it into locking mode. The user then feeds the excess webbing back into the retractor, while pushing down on the seat until all the slack is out of the webbing. If the CR has a lock-off, switching the belt to ALR mode should not be necessary for a firm installation.

If these features are not available, a locking clip must be used to keep the vehicle belt in a tight pre-crash position on the CR. Locking clips may be difficult to use and can be misused, so it is best to take advantage of vehicle lockability features or CR lock-offs first. When installing a rear-facing CR with a three-point belt, there are some cases when the shoulder belt pulls up and tips the CR to the side after it is locked and tightened. It may be necessary to use a locking clip to keep the belt from shifting through the latchplate, which causes the tipping. However, this does not happen with every rear-facing CR in every vehicle or seating position, and a locking clip should only be used when a problem with tipping has been documented.

There have been cases documented where a child pulled on an unused or unlocked safety belt, wrapped it around his or her neck, switched the retractor into ALR, and was strangled by the belt. For this reason, it may be advisable to switch retractors to ALR mode and remove slack in unused belts or belts secured with lock-offs to prevent these incidents.

FMVSS 208 currently includes a “sunset” provision to remove the lockability requirement in 2012 for seating positions with LATCH anchorages. This will cause a problem for CRs that either do not install well with LATCH or are intended for higher weight children who exceed the recommended weight limits of the vehicle manufacturer for installation with LATCH. In these cases, the locking clip will need to be used, once again increasing the difficulty of installation and likelihood of misuse. SafetyBeltSafe U.S.A. has petitioned NHTSA to remove the sunset clause from the regulation. (9/07)

Locking clip

Metal hardware used to hold the lap portion of a lap-shoulder belt tightly through a CR belt path during normal driving by securing the lap belt webbing to the shoulder belt webbing next to the latchplate. This piece of hardware is also called a “regular” locking clip. Locking clips are for pre-crash positioning and are not designed to hold the belt in a sudden stop or crash. In those situations, the emergency locking retractor (ELR) will activate to lock the belt. Locking clips should be placed within an inch of the latchplate and never on the side opposite the buckle. They are typically used with lap-shoulder belts having free-sliding latchplates but may be used with other lap-shoulder belt systems as well (see Lockability). Locking clips should not be used on manually adjusted lap-only belts. If the belt slips because the locking latchplate is tilted relative to the belt webbing, the locking clip is not strong enough to keep the belt from slipping in a crash. A locking clip is not needed if a vehicle lockability feature is activated or if the CR provides its own locking feature, such as a lock-off. Locking clips are interchangeable, so that a clip from one manufacturer can be used with a product from another. However, regular locking clips cannot be used when a belt-shortening clip is needed. Locking clips should not be used with a belt-positioning booster or when a person is using only a safety belt. (9/07)

Locking clip, heavy-duty
Locking latchplate
Lower anchorage

One of two horizontal rigid bars 6 mm in diameter and 25-40 mm long specified in FMVSS 225, installed in vehicles in or near the seat bight, and to which one of two lower attachments is connected to secure the lower part of the CR using LATCH. See also Child restraint fixture, Funnel guide.

Lower attachment

One of two hardware assemblies on a CR with LATCH, possibly including webbing (or a single assembly with a connector at each end) that enables the CR to be securely fastened to one of two (or both) lower anchorages. Those using webbing and a manual adjuster are referred to as flexible attachments, while those built into the CR base, fixed at 280mm (11 in) apart, and equipped with a telescoping adjustment are called rigid attachments.

Lower Universal Anchorage System (LUAS)

The Canadian term for a system similar to LATCH.

Manufacturer's instructions

Any deviation from the intended application and use of a CR that might reduce its protective performance. Detailed assessments of CR installation and use, including choice of restraint, indicate that 80-95% of CRs are misused in some way. From one perspective, these survey results may discourage caregivers into thinking they could ever choose, use, and install CRs effectively, so why should they try? On the other hand, these high reported misuse rates may encourage caregivers to read and carefully follow the manufacturers’ instructions or to seek professional help. The important point to remember is that, while the best protection comes from a perfect CR installation, field data indicate that improperly used CRs still offer some level of protection in most crashes, and overall CRs are very effective at reducing serious injuries and deaths.

A problem with most misuse surveys is that they do not differentiate among various levels of misuse. While safety experts generally agree on the worst cases of gross misuse (child not restrained in CR, CR not attached to vehicle, infants facing forward), there are many other types of misuse with a range of potential consequences and not enough data to agree on how to categorize them as minor, moderate, or gross. Although some types of misuse may have little or no effect in low-speed crashes, other common mistakes can make the difference between life and death, especially in a severe crash. For example, a common misuse is loose harness straps. A small amount of slack might not affect the outcome in a minor crash, but a large amount of slack might allow ejection in a severe crash. In addition, several minor misuses may add up to more severe compromises in protection. The best approach is to identify and correct misuses that are known to severely compromise CR performance and to address others by explaining the concepts of crash protection and advising parents about the direction to aim when perfection cannot be achieved. For further information on the crash dynamics and the consequences of misuses, see Weber, 2000.

Advances in design have made CRs easier to use, with the intent of reducing misuse. The NHTSA Ease of Use Rating system has also led to improvements in the adjustability of harness systems and tether straps in many CRs. In addition, LATCH systems have reduced many of the problems in securing CRs to vehicles, but at the same time new types of misuse have arisen. For example, parents are attaching tethers to cargo hooks or securing CRs using both vehicle belts and lower LATCH attachments. It is also important that CR manufacturers evaluate misuse potential whenever new designs are considered. (7/06)

No-rethread vs. rethread harness

A no-rethread harness does not require removing the straps from the splitter plate and locating the appropriate set of harness slots through which to “rethread” the harness. The system employs another method for raising or lowering the level of the straps, usually a guide that can be disengaged to move the harness level and then engaged to lock the harness height into place.

A rethread harness achieves the same purpose by permitting removal of the harness end from the metal splitter plate on the safety seat back and providing a set of visible slots are various levels through which the harness end can be threaded and then attached once again to the splitter plate.

Padded inserts, blankets, and bulky clothing

Safety seats are crash-tested with the padding/lining/covers with which they are sold. Anything else added is likely to compromise protection for the child. Thick, soft, compressible material should not be placed behind or under the child nor in between the child and the harness shoulder and lap straps. The primary concern is that the padding may compromise protection in a crash. Blankets or inserts may interfere with proper harness routing. Soft foam padding or fluffy blankets will compress in a crash and leave the harness slack on the child, allowing excessive movement or even ejection. Bulky jackets and snowsuits can have the same effect, while “baby bags” without legs and blankets wrapped around the baby before harnessing do not allow for proper routing of the crotch strap. It is also acceptable to put firm padding, such as a rolled receiving blanket, between a small baby and the sides of the shell as a space filler. No padding should be placed between the baby and the harness with one exception: a folded washcloth may be wedged between the crotch strap and the infant’s crotch to help prevent slumping for a very small newborn, unless the manufacturer of the safety seat disallows it. Padded inserts and pillows that come with a CR must be tested as part of the product to the requirements of FMVSS 213, including a flammability test, so use of these as described in the instructions is permitted. Some infant inserts MAY be used; others MUST be used. Some have a weight limit; others do not. For many seats, padding is an integral part of the crash protection at certain weights; therefore, careful reading of the instructions is essential. An extreme example is the Clek Infant Thingy. Used with the Foonf or Fllo convertible seats by Clek, the lower limit of the seat moves from 14 lbs and 6 months to 5 lbs and no minimum age. It is particularly important not to place additional padding or use after-market head protectors in a safety seat with a young infant. The safety seat is designed to position the child at an angle that allows best crash protection while also allowing the babyÕs head to lie back naturally so that the child’s airway (which is very small in a newborn) remains open. Adding additional padding can change this alignment and could potentially compromise the child’s airway. Other products sold as aftermarket accessories have not undergone crash testing with the product. Thus, they are not recommended. Some CR manufacturers are marketing CR accessories, including these products as well as toys to attach to the CR, which have been tested with their CR according to FMVSS 213 regulations. These same manufacturers prohibit the use of any accessories, including inserts between the child and the safety seat, unless provided by that manufacturer. Clothing worn by the children also present potential compression and harness routing problems. It is best to have children travel without coats, to put coats on backwards, or to add a blanket over the child after the harness has been buckled. Jackets that are worn the regular way should be no heavier than lightweight fleece fabric or be unfastened to allow contact between the child and the harness or belt. A useful test to see if a jacket is too bulky is to buckle the child into the harness with the coat on and adjust the harness to a snug fit (do the pinch test), then unbuckle the harness, remove the coat and re-buckle. If slack has been introduced to the harness, the jacket is too bulky. Those who work in the Safe Sleep field note that babies can suffer if they re-breathe air and caution about putting materials near the face. For this reason, blanket rolls should be no higher than shoulder level. (7/06; reviewed/edited 11/15)


Padding is required by FMVSS 213 in the area contactable by the head only for CRs certified for use by children under 22 lbs, including both infant-only and convertible. Child seats would therefore be exempt. In Canada, however, padding around the head is required for all CRs and is the reason some combination seats sold in Canada are different from those sold in the U.S. Both standards require at least a half inch thickness of “slow recovery, energy absorbing material,” but, ironically, the test used to certify the foam will not allow such material. Instead it specifies very soft, compressible material with virtually no energy-absorbing (EA) capability. Some manufacturers have installed EA foam, such as expanded polystyrene, next to the shell and put the mandatory flimsy padding on top, but this requires special shell designs to accommodate the extra thickness. EA padding is not required on shields, and few have it.

Rear-facing child restraint

A restraint that is installed so that the child faces the rear of the vehicle, including both infant-only and convertible CRs. Rear-facing child restraints are the most effective of all types of child restraints. In frontal crashes, which are the most frequent and severe, the primary restraint surface is the back of the shell. The shell supports the head and distributes impact forces over a wide area to the infant’s strongest body region, the back. It also lets the head and torso move together, which prevents excessive stretching of the neck (see Rear-facing vs. forward-facing). The harness provides secondary restraint on rebound during frontal crashes and keeps the child within the restraint during other types of crashes.

Because rear-facing CRs are the most effective restraint available, the American Academy of Pediatrics recommends that “children should remain rear-facing until reaching the maximum weight for the seat, as long as the top of the head is below the top of the seat back” (see AAP, 1999). To prevent severe spinal injury, children should remain rear-facing until they are at least one year old and weigh 20 lbs, but safety experts recommend 18-24 months and up to 35 lbs, depending on the restraint used. Infants will need to switch from an infant-only CR to a rear-facing convertible to stay rear-facing the recommended length of time. However, consumers should not be confused by forward-facing weight ranges required to be listed on convertibles by FMVSS 213. The minimum weight is only that for which the CR has been certified forward facing, not the weight at which the child should be turned to face forward.

All convertibles currently sold in the US are certified for rear-facing use for children up to 30 to 35 lbs. For larger children who are medically fragile (low bone density, non-ambulatory cerebral palsy, juvenile rheumatoid arthritis), caregivers can apply to NHTSA for permission to import a rear-facing child restraint from Sweden that can accommodate children up to 55 lbs (25 kg) rear-facing. Contact: NHTSA Chief Counsel, NDD-112, 400 Seventh, St. SW, Washington, DC, 20590, 202-366-2992. (1/07)

Rear-facing CR in front of armrest

Older instructions from Evenflo warned against placing a rear-facing seat in front of a fold-down armrest. They no longer issue this warning and have retracted it for all products. Currently, there are no known vehicle manufacturers with warnings against the practice, so it should not be considered a factor in child restraint installation. (6/08)

Rear-facing CR resting against front seat or dashboard

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.

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 currently provides. Alternately, instructions for a few rear-facing child restraints state that they should not touch the front seatback in order to perform properly. One discontinued convertible model was designed to rotate to a more upright position during impact, and some infant-only restraints are expected to rotate away from the front seatback in a severe rear impact if given sufficient initial clearance. When a rear-facing child restraint is tested to FMVSS 213, there is nothing in front of the restraint that it can contact (see picture in Angle of recline, rear-facing).

Rear-facing tether
Rear-facing vs. forward-facing

Safety experts and the American Academy of Pediatrics recommend that children remain rear-facing as long as possible and never travel forward-facing before they are 1 year old and also weigh at least 20 pounds to reduce the risk of serious neck injury and lifelong disability. All new convertible seats available today allow a child to remain rear-facing until they weigh up to 30 or 35 lb, depending on the model.
When the child is rear-facing, the head, neck, and thorax are restrained together by the back of the CR in a frontal crash. There is little or no relative motion between the head and torso that could load the neck. If the same child were facing forward, the harness would restrain the torso, but the head and neck would pull and rotate forward, leading to the potential for serious upper spinal injury.

There are many misunderstandings and misconceptions about rear-facing vs. forward-facing that lead even the best intentioned parent or pediatrician to believe a child is “safe” facing forward when he is still very young. These come from obsolete ideas and advice that may still appear in older pamphlets and pediatric literature and are not the current recommendations of the American Academy of Pediatrics.
Real-world experience has also shown that a young child’s skull can be literally ripped from her spine by the force of a crash. The body is being held in place, but the head is not. When a child is facing rearward, the head is cradled and moves in unison with the body, so that there is little or no relative motion that might pull on the connecting neck.

The most common misunderstanding is that a child is ready to travel facing forward when his neck muscles are strong enough to support and control his head. However, when a car hits something at 25 to 30 mph, it will come to a stop at a negative acceleration rate of from 20 to 30 G. Because of the time lag between when the vehicle stops and an occupant stops, and the fact that the head of a forward-facing adult or child is still free to move relative to the restrained torso, the head may experience as much as 60 or 70 Gs acceleration for a brief moment. Even the strong neck muscles of military volunteers cannot counteract such forces. Instead, the rigidity of the bones in the neck and strength of the connecting ligaments (not the muscles) hold the adult spine together and keep the spinal cord intact within the confines of the vertebral column.

Very young children, however, have immature vertebrae that are still partly made of cartilage. These are soft and will deform and/or separate under tension, leaving just the spinal cord as the last link between the head and the torso. According to documented research, autopsy specimens of infant spines and ligaments allow for spinal column elongation of up to two inches, but the spinal cord ruptures if stretched more than 1/4 inch. Real-world experience has shown that a young child’s skull can be literally ripped from her spine by the force of a crash.

Another aspect of the facing-direction issue that is often overlooked is the additional benefit a child gains in a side impact. Crash testing and field experience have both shown that the head of a child facing rearward is captured by the child restraint shell in side and frontal-oblique crashes, while that of a forward-facing child may be thrown forward, around, and outside the confines of the side wings. Field data show better outcomes for rear-facing children than forward-facing children, even though most CRs are not specifically designed to protect children in side impact.

Some older convertible CRs indicated in their instructions that a child should face forward when her feet touch the vehicle seatback or when the legs must be bent due to lack of space. This prohibition is not justified by any crash experience or any laboratory evidence, and these instructions have now been revised. There have not been any crashes documented in which rear-facing children sustained leg injuries because they were rear-facing. Even if this were the case, broken legs are easier to fix than broken necks. The only physical limit on rear-facing use is when the child’s head approaches the top of the restraint shell (see Height and weight limits). At this point, she should be moved to a rear-facing convertible restraint, or, if the child is already using one and is over one year, to its forward-facing configuration.

There are no magical or visible signals to tell parents, pediatricians, or technicians when the risk of facing forward in a crash is sufficiently low to turn the child around. In an international research and crash review conducted several years ago, the data seemed to show a change in outcome at about 12 months between severe consequences and more moderate consequences for the rare events of injury to young children facing forward in a CR. At the time, one year old was useful as a simple benchmark, but now the message is to keep the child facing rearward as long as possible within the weight and height limits of the CR. This may be as long as 18 to 24 months.
Parents and pediatricians need to know what the real reasons for extending the rear-facing period, in order to be able to make an informed judgment. For research documentation, see Weber, 2000. See also Rear-facing child restraint. (7/06)

Recline angle
Recline adjustment mechanism

A device built into the safety seat to assist with achieving proper recline in rear-facing or forward-facing mode.


“Riding down the crash” with the crushing vehicle decreases the severity of injury, because the crushing of the front end lengthens the stopping time and distance of the occupants who are attached to the frame by belts. Injury increases as the speed at impact increases and the more abruptly the occupants come to a stop. To take advantage of vehicle ride-down, the occupant must be tightly belted to the vehicle, and the fewer links there are, the better. For children, both the vehicle belt holding the CR and the harness holding the child must be snug, while built-in CRs have only the harness link and therefore perform very well. If occupants are not belted to the vehicle, there is no ride-down, only hard impact with the vehicle interior. Air bags also provide ride-down, independent of vehicle crush, as the occupant gradually pushes the air out of the bag through small designed-in openings. See also Energy absorption.

Seat bight

The intersection of the vehicle seat back and bottom cushion (or “crack”), where vehicle belts frequently emerge and where LATCH lower anchorages are placed. “Forward-anchored belts” emerge from the seat cushion, well in front of the bight, and make secure CR installation difficult, if not impossible.

Seatbelt syndrome
Seating position

The front seat is a more dangerous environment than the rear seat for two reasons. First, recent crash data show that children 15 years and under have a 40% lower risk of serious injury in the back seat compared to the front seat (Durbin et al., 2005). This increased risk occurs because the front passenger compartment is more likely to have intrusion than the back seat area in frontal crashes, which are the most common type. Consequently, FMVSS 213 requires manufacturers to say in their instructions that, “according to crash statistics, children are safer when properly restrained in the rear seating positions than in the front seating positions.”

Second, air bags can cause serious or fatal injuries to children in the right-front passenger seat. Because “properly restrained” infants have been killed by air bags, even in low-speed crashes, a rear-facing infant must never be restrained in a seat with an active air bag. Many unrestrained older children have also been killed because they were too close when the air bag deployed. Vehicle manufacturers are phasing in features that will turn off the air bag when a child is in the front seat or allow it to deploy with less force. However, because these systems that detect a child in the front seat are new, they have not been demonstrated to be foolproof, and, because it may not be clear whether a vehicle is equipped with these sensors or with a less aggressive air bag, the universal recommendation to avoid placing children in the right-front seat still stands.

If there are more children than rear seating positions, the most appropriate child to put in the front seat is the one in a forward-facing CR with internal harness, which will keep the child well back and away from the instrument panel and/or air bag. The harness must be snug, the CR firmly installed, with top tether if possible, and the vehicle seat moved as far rearward as possible. A child in a rear-facing CR should never be placed in a front seating position with an air bag.

In general, the single safest place in the car is the center rear seat, because it is farthest from the outside of the vehicle. In any given crash, however, a different seat may be the safest, such as a left outboard seat in a right side impact. There are several reasons the center seat may not be an option. Many small cars do not have center seats; it is sometimes not possible to tightly install a CR in the center rear; belt-positioning boosters require lap-shoulder belts, which may not be available in the center; and, if there are two children, it may be necessary to separate them for behavioral reasons or because two CRs cannot be installed next to each other. The left and right seating positions are very similar in injury risk, but the right side might be a better choice for one child with one adult. The child can see the driver and can be taken or get out of the car on the side where there is no traffic. Using the center or right rear seat will also minimize the chance of injury to the child from driver seatback collapse in a severe rear impact. Although most vehicles do not have LATCH anchors for the center seating position, CRs equipped with LATCH can still be installed in the center with the vehicle belt and a top tether, if appropriate.

A difficult choice for an older child is when the seating positions available are a lap-only belt in back or a lap-shoulder belt in front, with or without a belt-positioning booster. The child in the lap-belt has an increased risk of injury because there is no upper torso restraint, while the child in the front seat has an increased risk of injury because she is sitting in the more dangerous seating position. Overall, field data suggest that the injury risk for a child properly restrained in the front seat is about the same as the child improperly restrained (lap-belt only) in the back seat. Both choices are riskier than a properly restrained child in the rear seat. (7/06)

Sewn-on latchplate

A latchplate that is sewn on to the end of the safety belt webbing.


The “seat” portion of a CR that holds the child in position relative to the harness. Most current products use shells constructed of reinforced plastic that withstand and help distribute crash forces. For infant-only restraints, the shell usually comes with a separate base, and the shell can be used alone or with the base for most of these products. However, at least two current models of infant-only restraint do not allow use of the shell without the base. Convertibles may have a non-detachable base on which the shell rotates to provide different angles of recline or a base that can be detached to improve fit in the vehicle or when transformed into a belt-positioning booster. (9/07)

Shields on safety seats

The original crash-tested forward-facing safety seat was the Ford Tot-Guard, a 2 -piece CR– large shield with a hard plastic seat—for children 1 year & 20 lbs. to 50 lbs. Subsequently, shields— with or without harness straps, t-shaped and tray-shaped, were used by numerous CR manufacturers. In general, the 5-point harness replaced these styles after 2009. The occasional model with a shield to restrain the child and absorb crash forces has emerged outside the U.S. Shield boosters developed originally because few vehicles had shoulder-lap belts in the back seat until after the SBS USA petition led to mandatory shoulder-lap belts in outboard seating positions in 1989.

Shoulder belt guide

A feature on a booster seat that is intended to improve the routing of the shoulder belt on the child’s shoulder. It can be a slot, hook, loop, or clip attached to the side of a highback belt-positioning booster, or a clip on an adjustable strap attached to a backless booster. The shoulder belt guide should position the belt on the middle of the child’s shoulder and be as close to the child’s neck as is comfortable. It is more dangerous for the belt to be positioned too close to or even down on the child’s arm than close to the neck. The highback booster guides should have several positions for different sizes of children, and they should not restrict the retraction of the shoulder belt. When using these guides, keep the belt going as straight as possible from the lap to the upper anchorage to minimize belt slack. With either a highback or a backless booster, if the shoulder belt does not chafe the neck, it is not necessary to use the guide. (3/07)

Shoulder belt positioner

Built-in or aftermarket devices that are intended to place and keep the vehicle belt crossing the shoulder between the neck and arm. Systems built into the vehicle include adjustable upper anchorages and plastic clips that attach to the side of the vehicle seat with a cord. These systems do not change or improve the position of the lap belt. Aftermarket shoulder belt positioners are not covered by Federal safety regulations, and those that connect the lap portion to the shoulder portion of the vehicle belt are not recommended for children or adults. NHTSA has conducted tests of three of these products and concluded that all of these devices produce some degradation in the performance of the lap-shoulder belt system by either inducing slack in the belt or by raising the lap belt off the pelvis onto the abdomen. Most belt-positioning boosters have a shoulder belt guide or clip on the side (of highbacks) or a plastic clip on a strap (for backless ones) that may improve the position of the shoulder belt. This guide need not be used if the shoulder belt fits the child correctly without it. For children, BPBs are recommended instead of shoulder belt positioners primarily because the former also improve lap belt fit and performance in a crash, but also because the child will be more comfortable on the shallower, higher seating platform. For more information see the 5-Step Test. (3/07)

Side air bag

See Air bag.

Sliding latchplate

latchplate on a lap-shoulder belt that does not impede belt movement so it slides easily, changing the lengths of the lap and shoulder portions and therefore, does not meet the “lockability” requirements of FMVSS 208.

Snug harness

The motion of an occupant when the hips slide under the lap belt, so that the belt applies crash forces to the soft abdominal area between the pelvis and ribs. This motion is more likely to occur when the upper body is restrained with a shoulder belt, but it can also occur with a lap belt alone if the occupant is slouching. In this case, the upper body will fold forward over the lap belt and the lower (lumbar) spine may break at the point where it is forced to bend. The injuries that result from submarining are called “seatbelt syndrome.”

Switchable latchplate
Switchable retractor

A vehicle belt retractor that can be changed from an emergency-locking retractor to an automatic-locking retractor for tight installation of a CR. In most vehicles, the retractor is switched by pulling the belt all the way out of the retractor, which causes the retractor to change into automatic-locking mode. In a few vehicles, the locking mechanism is activated with a switch located near the door. See also Lockability. This type of retractor sometimes causes problems when installing a rear-facing CR where the shoulder belt must be routed through the belt path. After the retractor is switched and the belt pulled tight, the shoulder belt may begin to lift up one side of the CR, making it tip. If the belt cannot be adjusted to prevent the tipping, it may be necessary to unbuckle the vehicle belt, let it retract and switch into ELR mode, and use a locking clip to hold the lap portion of the belt tight. There are two other cases when a switchable retractor might be changed to ALR mode. One is when a child in a booster seat or safety belt is too active to sit with the lap-shoulder belt positioned correctly or too inexperienced to keep the belt snug on his/her body. The retractor can be switched to automatic-locking mode, so the child cannot move around as much and the belt will stay snug. When this action is necessary, however, the growing number of forward-facing harness restraints with higher occupant weight limits should be considered the preferred solution. The second case is when a lap-shoulder belt is unused in a seating position, because the CR is secured with LATCH or no occupant is present. Caregivers may choose to buckle the belt, switch it into automatic locking mode, and feed the belt into the retractor, so the belt is not a strangulation hazard for a child in a nearby seating position. (6/08)

Top tether

An assembly consisting of a top tether strap, attached at or near the top of a CR, together with a length adjuster and a top tether hook, that is used with either a vehicle belt or lower LATCH attachments for complete installation of a CR in a vehicle. For a forward-facing CR, the top tether keeps it from rotating forward in a frontal crash and significantly decreases head excursion. The tether can also improve installation stability, especially when the vehicle belt cannot be tightly secured due to incompatibility problems. Top tethers can also be used with rear-facing CRs (see Top tether, rear-facing), and, in Scandinavian countries, large rear-facing restraints are equipped with a different type of tether attached to the lower part of the CR. LATCH consists of a top tether along with lower attachments that may be configured much like a lower tether. As of September 1999, new head excursion requirements in FMVSS 213 made top tether straps, either attached or with attachment instructions, necessary on almost all convertibles, child seats, and combination seats sold in the U.S. Those products that can meet the new requirements without a tether have offered them as options. If a CR is equipped with a top tether that is not being used, parents should be encouraged to find or install a top tether anchorage in their vehicle(s). When not in use, the top tether hook and anchorage hardware, if included, should be secured to prevent them from injuring a child in a crash. The correct anchorage location for the top tether can be found either in the vehicle owner’s manual or in the instructions provided by the vehicle manufacturer with the tether anchorage kit, available from dealerships. Use only tether anchorage locations specified by the manufacturer. For older CRs, a tether kit, which includes the webbing strap and the means to attach the strap to the CR, may be obtained from the manufacturer. The instructions specify whether it must be attached to the CR frame, an add-on metal rod, or a slot in the plastic shell. It is essential to order the correct kit based on the exact model and date of manufacture. Some of the hardware in the CR and vehicle kits may be the same, but certain pieces are not interchangeable. If a threaded nut or receptacle is provided in the vehicle, the matching bolt must be used. Using the bolt from the CR manufacturer’s tether kit could strip the threads. If the tether bolt is screwed into a small nut, a large washer must be placed between the nut and the back of the mounting surface to keep the nut and bolt from ripping through the hole. The metal bracket (the only visible part of the anchorage hardware after installation) must be shaped so it accepts the hook on the end of the tether strap. For a comprehensive resource on LATCH, including tether use and anchorage installation, see Stewart et al. 2007.

Top tether, rear-facing

Only a few CRs 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 over 30 years of crash 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 (see Rear-facing CR resting against 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. Finally, tests conducted by a competitor a few years ago showed that dummy neck loads increased significantly when the restraint was tethered to the floor in both frontal and rear impacts. This would be more of a concern with the youngest infants than with children over 9 months to a year, but the competitor decided not to offer rear-facing tethers. The restraint models on which the rear-facing tether is offered, however, can accommodate children up to 2 years old and more 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 child’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 children are carried rear-facing, the chance of a child’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. Britax also acknowledges that one can route the tether rearward (Australian method) to the normal top tether anchorage, but this configuration has been given second priority. Of the two methods, this one is likely to have the most benefit in a frontal crash if there is rotation room in front of the child restraint. In practice, however, convertible restraints barely fit into back seats anyway, so the rearward tether may have limited use, except in vans.

Top tether anchorage

Hardware component, such as a ring, bar, bracket, or webbing loop, and its underlying structure in the vehicle, either user-ready or aftermarket-installed, to which a top tether is attached. Also called a “tether anchor.” For detailed information on tether anchorage installation, see Stewart et al. 2007.

Top tether hook

A metal connector specified by FMVSS 213 to attach a top tether strap to a top tether anchorage.

Top tether strap

A straight or V-shaped length of webbing attached at or near the top of a CR as part of a top tether assembly.

Top tether with highback booster
Twisted harness strap

Harness straps are designed to spread the force of a crash over a reasonable surface area while the child gradually rides down the crash. If the straps are twisted, the loading surface becomes narrower, which can increase the possibility of injury.

Twisted vehicle belt

Vehicle owner’s manuals usually warn against twisting vehicle belts. The primary reason is that belts work best if they distribute force over a wider area, and twisting belts reduces the area available for distributing force on the occupant. Another reason is that twisted belts may not slide through a latchplate, preventing snug fit around an occupant or secure installation of a CR. Twisting belts also reduces webbing strength. Laboratory tests conducted by IMMI Child Restraints in 1998-99 showed that the average strength of vehicle belt webbing, pulled until failure, gradually reduced depending on the number of full twists: 1=6%, 2=11%, 3=20%, 6=40%. When the webbing was soaked in apple juice or cola, the strength degraded slightly more than untreated webbing. When other samples were twisted and later untwisted, the webbing returned to normal strength. Vehicle belt webbing is strong enough to withstand pull tests of over 6000 lb of force. This is 3 to 4 times the strength needed to restrain a 60-lb child in a severe crash. Based on these data, CR experts advise that up to three full twists in belt webbing will not reduce its strength enough to risk failure when restraining a child in a CR. There are two situations that call for twisting vehicle belt webbing (up to three times) so that the CR can be secured properly. For lap-only belts, the locking latchplate may be resting on the CR at an angle, so that it does not stay locked. By turning the latchplate over once (a half twist) and inserting it into the buckle, the locking bar will be held in place and the belt will not slip. For lap-shoulder belts, the buckle location might need to be shifted to allow the buckled belt to be tightened. This can often be done by “shortening” the webbing attached to the buckle with one or two full twists. These techniques will not work if the webbing at the buckle end is very long or if the buckle is attached to a stiff cable. If the webbing is supported by a plastic sleeve, the caregiver may carefully cut through the sleeve and remove it. (6/08)

Vehicle belt enhancements

There are several innovative belt systems being installed in some vehicles that change the way the belts work in a crash. These features are primarily designed to improve protection for adult occupants in the front seat, and some are designed to work in conjunction with air bags. An emergency tensioning retractor (ETR), tightens the belt before the occupant loads it. An emergency-tensioning buckle (ETB) moves the buckle down and rearward. Both of these systems are triggered by the deceleration sensors that trigger air bags and are also called “pre-tensioners.” Energy management loops (EML), which are tucks sewn into the webbing with breakable stitching, or energy management retractors (EMR) gradually loosen the belt after the occupant loads it, to reduce the force on the adult chest and minimize the risk of broken ribs or ruptured organs. Both of these systems are called “load limiters.” A less expensive alternative to an EMR, now being considered for rear seats, is belt webbing with controlled elongation (see also Belt stretch). A belt pre-tensioner can be combined with an EMR to restrict and then allow controlled forward motion. Webbing grabbers are jaws that grip the belt webbing as it tries to pull out of the retractor. They prevent “spooling” that allows belt webbing to tighten on the retractor spool and generate slack. Webbing grabbers provide some of the effect of belt pre-tensioners at a lower cost and weight, especially in vehicles that do not already have an air bag crash sensing system. Vehicle belt pre-tensioners and load-limiting EMLs are found almost exclusively in front seats and must be replaced if activated. Load-limiting EMRs are used primarily in front seats, and it is not clear if they must be replaced if activated, as long as the belt is not otherwise damaged. Energy management loops were used in quite a few vehicles before air bags were added, but all vehicles with load-limiting EMRs also have air bags. Pre-tensioning ETRs have been used in European luxury cars since the mid-1980s, but passenger air bags are optional on many European models. Air bags can be deactivated in vehicles with load limiters that are designed to absorb energy at high forces, but some EMLs activate at a low force and would not provide good restraint without the air bag. In each case, the vehicle manufacturer should be consulted before deactivating an air bag.

Vehicle owner's manual

A book of information about features, their operation, and their use provided by the manufacturer in every vehicle. If they are missing, they can be purchased, and many are available online from the vehicle manufacturers’ Web sites. Recent manuals contain extensive information on installing CRs. Vehicle owner’s manuals should be checked to identify LATCH anchorage positions, to determine if a pair of inboard lower anchors can be used to secure a child restraint in a center-rear position, to find recommended child weight limits for securing a CR with LATCH, to learn how to install CRs with the available belt restraints, to see if outboard top tether anchors can be used with CRs in center positions, and to identify any seating positions where CR installation is not recommended. The manuals also contain information about air bag locations and any advanced sensors for deactivating air bags under certain conditions. Some older vehicle owner’s manuals may contain outdated or incorrect depictions of CR use and should be used with caution. Always consult the safety seat owner’s manual for specific use, such as belt paths to be used, etc., instead of relying on the generic information in the vehicle owner’s manual. (See also Installation tightness, Lockability). (6/08)


See Harness.

Webbing grabber
Webbing-sensitive retractor

A type of emergency-locking retractor (ELR) that is activated by a sudden pull on the belt. When the tension on the belt is released, the belt continues to slide freely in and out of the retractor. Some older ELR belts were exclusively webbing-sensitive, but current retractors have this feature as a back-up to activation by a sudden stop. The feature can cause confusion during installation, if the belt is pulled suddenly and appears to have a switchable retractor in the locked ALR mode. Test it by pulling the webbing out slowly to the end. If it does not lock easily with a gentle tug while retracting, it is a regular ELR and a locking clip may be needed.


5-Step Test. Boosters are for big kids. Resource #630. SafetyBeltSafe U.S.A., Altadena, CA, 19 Jan 2004.
American Academy of Pediatrics, Committee on Injury and Poison Prevention. Safe transportation of premature and low birth weight infants. Pediatrics May 2009, VOLUME 123 / ISSUE 5.
American Academy of Pediatrics, Committee on Injury and Poison Prevention. Safe Transportation of Newborns at Hospital Discharge. Pediatrics October 1999, VOLUME 104 / ISSUE 4.
Durbin DR, Chen I, Smith R, Elliott MR, Winston FK. Effects of seating position and appropriate restraint use on the risk of injury to children in motor vehicle crashes. Pediatrics 115:305-309 (2005).
Humanetics Innovative Solutions (formerly First Technology Safety Systems), Plymouth, MI. Product catalog online.
FMVSS 208. Occupant crash protection. Code of Federal Regulations, Title 49, Part 571.208. 1 October (current year).
FMVSS 213. Child restraint systems. Code of Federal Regulations, Title 49, Part 571.213. 1 October (current year).
FMVSS 225. Child restraint systems. Code of Federal Regulations, Title 49, Part 571.213. 1 October (current year).
Stewart DD, et al. The LATCH Manual 2019: Using Lower Anchors and Tethers for Child Restraints. 6th ed. Safe Ride News Publications, Seattle, 2009. Order information.
Transport Canada. How to Protect Children in Vehicles with Side Air Bags. Road Safety Fact Sheet # RS2000-06R. February 2001, revised March 2006. LINK
Weber K. Crash protection for child passengers. UMTRI Research Review 31(3):1-27 (2000).

Revised 12/03/08
Cheryl Kim, Senior Program Consultant
Kathleen D. Klinich, Technical Consultant
Kathleen Weber, Technical Consultant