Rear-facing Child Restraints

Both the American Academy of Pediatrics and the National Highway Traffic Safety Administration now recommend that children remain rear facing
until they outgrow their restraint. This means that most children can remain rear-facing through age 2 years, based on average child sizes and the capacity of most rear-facing convertible restraint products on the market. US crash data show that children aged 0–2 years are 5.53 times safer in a rear-facing restraint than in a forward-facing restraint in side impacts and 1.23 times safer in frontal impacts (Henary et al. 2007). These recent US data support Swedish data showing benefit for children rear-facing through age 4, with rear-facing restraints reducing AIS2+ injury by 90% compared with unrestrained children (Jacobsson et al. 2007, Isaksson-Hellman et al. 1997). Because earlier rear-facing child restraints did not accommodate larger children, older education materials may contain outdated information stating that children can begin using forward-facing restraints at age 1 or 10 kg (20 lbs), which is no longer considered a safe practice.

Types of rear-facing restraints

Two types of restraints, infant restraints and convertibles installed rear-facing, are commonly used to orient the child to face the rear of the vehicle. Infant restraints can only be used rear-facing and most have a separate base which remains in the vehicle to facilitate repeated installation (left figure), but most can also be used without the base and secured with the seatbelt (middle figure). The infant restraint base can be installed with either lower anchorages or the seatbelt. These products usually have a carrying handle. Traditionally, these products have accommodated children up to 9 or 10 kg (20 or 22 lb), but there are now many models that can accommodate children up to 13 kg (30 lb). A rear-facing convertible is shown in the right figure. These can be used rear-facing up to 13–20 kg (30–45 lb), then converted for forward-facing use. Convertibles tend to be larger than infant seats. While most children will outgrow their rear-facing restraint because they reach the allowable maximum weight limit for their use, some children will outgrow their rear-facing product because the top of their head is within 2.5 cm (1 inch) of the top edge of the child restraint back support. It is common practice to use an infant restraint for a newborn until it is outgrown by weight or seated height. For a product with a 9 or 10 kg (20 or 22 lb) weight limit, this means that most children would outgrow the device within the first year and should then be moved into a convertible child restraint used rear-facing.

Rear-facing restraints use an internal harness to secure the child into the shell. In a frontal impact, the restraint forces occur where the back of the child meets the restraint so that the restraining load is distributed across the entire back and head of the infant.
Infant seat with base installed Infant seat alone, installed with seatbeltRear-facing convertible installed with

The infant’s head is well supported in this mode, and the movement of the head and neck happen in unison with the torso during a crash to eliminate severe tension and flexion forces on the neck that can occur with forward-facing occupants. The video below shows the difference in kinematics between the same child restraint used rear-facing and forward-facing in a simulated frontal impact. Peak axial neck forces are four times higher in the forward-restraint compared to the rear-facing restraint.

Rear-facing vs. forward-facing

Using a rear-facing infant restraint facing forward can result in dangerous loading and possible ejection because the belt path has not been designed for loading in this mode. Similar consequences could occur if a convertible restraint is installed rear-facing using the belt path for forward-facing (or vice versa). Restraining an infant or toddler forward-facing too early increases the risk of injury to the spinal cord as the child’s disproportionately large/heavy head is stopped from forward motion by a tension load applied in the cervical spine.

Regulatory tests differ globally with regard to the extended rear-facing position. In Europe, dynamic tests for both frontal and rear impacts (R44/04) require additional attachment and stabilization elements to conform to the requirements. Swedish rear-facing child restraint designs differ from US products, in that they often use a support leg and strap attachment to the front seat or are placed in the front seat against the instrument panel with the airbag deactivated to limit forward rotation of taller or heavier children. These extra requirements are less known in EU countries outside Sweden, which may lead to a higher risk of incorrect installation. In addition, these seats are approved for use in specific vehicles, not across all models.

Rear-facing restraint recline angle
The angle of installation is one of the most critical factors for correct restraint of children riding rear-facing. If the restraint is too upright, newborn infants may not be able to breathe because their
Rear-facing recline angle
heads drop forward during travel. If the restraint is too reclined/flat, the child will not be effectively restrained by the back of the child restraint. Ensuring that the child’s head is in contact with the child restraint back support is also best for crash protection.

Focusing on crash protection, if the back support angle is more reclined than 45°, the reaction force to restrain the child in a frontal crash starts to be exceeded by the force projecting the baby upwards along the seatback and toward the front of the vehicle. As the child grows, gains weight, and can hold its head erect, a more upright restraint angle would provide better crash protection.

For the youngest infants, providing
the best crash protection must be balanced with providing an angle that prevents the head from flopping over and potentially pinching off the airway. A back support angle of 45° from vertical is considered the maximum angle that can achieve these two aims. To account for the differences in vehicle seat angle, child restraint manufacturers often provide a means to indicate and adjust the installation angle. At least one major child restraint manufacturer sets its target angle at 35° from vertical through the use of a visual indicator, while others specify angles closer to 45°. Unfortunately, indicators provided on rear-facing child restraints are primarily based on the angle where the restraint performs best in regulatory testing. Manufacturers may not fully consider that the angle providing the best orientation for a newborn may not be the best choice for a larger toddler. If the installation angle required by child restraint instructions places a newborn too upright, either a different rear-facing child restraint or a car bed should be used.

If a rear-facing restraint is installed in a rear seat with its back initially against the seat ahead, this will help limit rotation during a crash and provide improved protection, partly because the child restraint will not suddenly strike the seatback as it would if there were an initial gap (Tylko 2011, Sherwood et al. 2005). However, some child restraint manufacturers prohibit contact with the front seat because of concerns about adverse interaction between the child restraint and front seatback in a rear impact. In some vehicles with advanced airbags, vehicle manufacturers also prohibit contact between a rear-facing child restraint and the right-front passenger seat because it could interfere with occupant sensing systems.

Tethering rear-facing

Following practices common in Australia and Scandinavia, some rear-facing child restraints in the United States provide the option to use a tether to help secure the child restraint to the vehicle, although all rear-facing child restraints sold in the United States need to meet the federal regulation without a tether. FMVSS 213 does not include any testing of a rear-facing child restraint with a tether, nor does FMVSS 225 cover tether anchors that may need to be located forward and below a vehicle seating position for use with a rear-facing child restraint.

The Australian tethering method, shown on the left, routes the tether rearward, towards the back of the vehicle, to the standard tether anchorage used for forward-facing installations. This tethering more effectively limits forward rotation of the restraint in a crash, minimizes movement into the front seat, and allows the child to better ride down the crash with the vehicle. The traditional Swedish method, shown on the right, routes the tether down and forward to a point on the floor in front of the vehicle seat. This approach helps adjust the initial restraint angle and limits rotation towards the rear of the vehicle on rebound (Sherwood et al. 2005).

Australian and Swedish tethering methods

Tethering rear-facing child restraints: Australian method (left) and Swedish method (right).

In a laboratory study comparing the methods of rear-facing tethering, any type of rear-facing configuration (no tether, Australian tether, or Swedish tether) provided superior protection compared to forward-facing restraint with tether. Among rear-facing tethering options, the Australian tethering method produced the lowest accelerations and excursion to the dummy head and chest among the methods evaluated.  None of the tethering methods produced potentially injurious neck loads, based on the neck loading levels established in FMVSS 208, during the rear impact test events (Manary et al. 2006).

Rear-facing restraints in side impacts and other impact directions

As in frontal impacts, the most important priority for reducing injury in side impact is to minimize or eliminate the head strike. If the child’s head contacts something, it should be a surface designed to absorb energy and limit injury. A typical rear-facing restraint will rotate toward the struck side of the vehicle more than a forward-facing restraint simply because of the increased distance between the combined center of mass of the occupied restraint and the belt path. Despite this greater motion toward the intrusion, rear-facing child restraints are over five times better at preventing injury in side impacts than forward-facing child restraints (Henary et al. 2007). Most side impacts also have a frontal deceleration component so the occupant usually moves toward the front and side of the vehicle simultaneously. When this happens, the head of the child in a rear-facing restraint will be directed further within the protection offered by the side wings of the restraint. This differs from a forward-facing child restraint, where the child’s head tends to move forward and around the sidewings and be more vulnerable to injury from the intruding vehicle or door structure. Several laboratory studies have demonstrated that a more rigid installation between the child restraint and vehicle, such as that provided by rigid LATCH attachments, also works better to keep any child restraint in position and prevent the head from contacting vehicle interior components (Klinich et al. 2005).

In rear-end and rollover crashes, the shoulder straps act to contain the child within the rear-facing restraint, which may rotate up against the vehicle seatback. This motion was originally touted as a benefit by the early designers to protect the infant from flying debris (Feles 1970). Since most rear-facing restraints are now larger and taller, this gives them greater potential to allow contact between the child’s head and interior vehicle components in a rear impact or rollover. However, injuries from this mechanism have not been documented in the field.

Harnesses and fit

Most rear-facing child restraints are now equipped with a five-point harness, although the original designs for rear-facing infant restraints were usually equipped with a three-point harness that did not include pelvic straps. Premature and newborn infants may be so small that many rear-facing restraints seem too big. Manufacturers have added lower shoulder harness positions and greater harness adjustability to improve the fit for tiny infants. Some child restraints come with padded inserts that position the infant’s body for improved harness fit and offer lateral support, but are removed for use with older children. Padding that pushes the infant’s head toward its chest should not be used. If the infant’s head or body needs lateral support beyond that provided by the child restraint, padding can be placed between the infant and the side of the restraint. Firm padding, such as a rolled towel, can also be placed between the infant and the crotch strap to keep the infant from slouching (AAP 2012). Supplemental thick, soft padding, which has not been provided by the child restraint manufacturer, should not be placed under the infant, behind its back, or between the infant and the shoulder straps. Such padding will compress during an impact, leaving the harness loose on the infant’s body and allowing increased sliding upward/ forward toward the front of the vehicle and increasing the risk of occupant ejection.

In a rear-facing restraint, shoulder straps should be routed to restraint slots that are at or below the shoulders of the child. If shoulder straps are positioned above the shoulders of a child in a rear-facing restraint, the child can slide up the seatback during impact so the head is beyond the top of the restraint, increasing risk of injury from head contact. Smaller babies’ heads may not reach the top of the restraint, but they could experience higher loading through the shoulders when stopped against the shoulder straps. Loose harnesses increase the chance of ejection and lead to increased loads once the child begins loading the harness. Use of a chest clip helps keep the harness positioned on the shoulders but cannot compensate for a loose harness during a crash.

Rear-facing restraints and frontal airbags

Frontal impact airbags and rear-facing child restraints do not mix. Even with advanced airbag systems, rear-facing restraints should never be installed in the right-front passenger seating positions. Installing any type of rear-facing child restraint in a seating position with a frontal impact airbag carries a high risk of injury or death during a crash. Frontal impact passenger airbags are stored in the instrument panel and need a certain amount of space in which to inflate before they begin to act as energy-absorbing cushions for larger occupants. A rear-facing restraint in the front seat places the child’s head and body very close to the airbag hardware. When current airbags deploy in a crash, whether severe or moderate, they emerge in a small folded package at very high speed—as much as 300 km/h (186 mi/h). If an airbag hits the back of a rear-facing child restraint while it is still inflating, it will strike with considerable force.  Accelerations measured at the heads of infant dummies in this situation range from 100 to 200 g, (Weber 1993, Klinich et al. 2002) with 50 g considered the threshold for injury for children represented by a 6-month size dummy (Klinich et al. 2002, Melvin 1995). The video below shows the initial impact of the airbag into a rear-facing child restraint, which laboratory measurements have demonstrated is the cause of fatal head injury in crashes. Although the airbag could also propel the infant and rear-facing child restraint into the vehicle seatback, the head injury from the airbag would already have occurred with the initial airbag contact into the back of the restraint.

Airbag deploying into rear-facing child restraint