Forward-facing child restraint systems

There are two main types of harnessed restraint systems that face the child toward the front of the vehicle. One is a convertible child restraint used forward-facing. The other is referred to as a combination child restraint. Combination seats are initially used with a harness; the harness is then removed to convert the restraint into a belt-positioning booster. In addition, a few products have been designed for only forward-facing harnessed use; others, called "all-in-one" or "3-in-one" products, switch from rear-facing to forward-facing-to boosters.

Convertible installed forward-facing with latch

combination installed with seatbelt

Historically, forward-facing restraints were made for use with a harness for a child up to only 18 kg (40 lb). However, many current models now accommodate children up to 30 to 40 kg (65 to 90 lb) using the harness system. These higher-weight harness systems may include higher slots for routing the harness straps at or above the shoulders of a larger child, as well as higher seatbacks that need to extend to a height at or above the child’s ears to protect against rearward bending of the neck. Forward-facing child restraint types can be installed with a seatbelt or LATCH lower attachments. However, because the design strength limit of vehicle lower anchors is 290 N (65 lbs), forward-facing child restraints may require seat belt installation with children at the upper end of the weight range. In addition, all current forward-facing child restraints recommend use of the tether with any installation to reduce head excursion during a crash, and some manufacturers require tether use for the heavier children.

Harnesses and Shields

The ability of a forward-facing restraint to provide effective protection depends on harness fit and snugness as well as tight coupling to the vehicle. Current child restraints are usually equipped with a five-point harness, which are preferred because they permit a snug fit around the child. Previous styles of forward-facing child restraints used a tray shield and shoulder straps; they are no longer sold in the US because they did not always permit a snug fit.

5-point harness

Tray shield

The five-point strap harness arrangement is generally styled after military and racing harnesses. Straps go over each shoulder and the lower portions form a lap belt across the thighs as two latchplates connect to a central buckle. The buckle, which is on the end of the crotch strap, is routed between the child’s legs, and serves to hold the lap straps down on top of the thighs, so it should be as short as possible. Most current products have a single pull harness adjustment strap or knob that makes it easier to tighten the harness so it is snug around the child compared with earlier designs. Loose harness straps will allow the child greater movement toward vehicle interior surfaces and generate higher loads on the child when the system finally pulls up tight to resist movement. Failure to buckle the harness or route the harness properly could result in ejection or serious injury to thoracic and abdominal organs.

The shoulder straps of the forward-facing harness should be routed to shell slots located at or above the child’s shoulders. For forward-facing restraints, erroneously placing the harness shoulder straps in slots located below the shoulders has the consequence of introducing slack in the harness, as the child’s torso can move forward before the straps begin restraining the shoulder and also creating increased compression loading in the spinal cord. Using harness slots not specified for forward-facing use may lead to child restraint shell failure, as some lower slots on convertible restraints are not reinforced for loading in frontal mode.

Neck injury in forward-facing child restraints

A transition to a forward-facing child restraint should not be celebrated, but delayed as long as possible. A child “graduating” to facing forward actually experiences a decrease in protection from riding rear-facing, which is the safest mode of restraint available for children. While education about the benefits of extended rear-facing restraint use has become more widespread, there are still misconceptions even within the medical community about the appropriate timing for the transition to forward-facing restraints. Analysis of field data shows a 55% reduction in injury risk for children under age 2 using rear-facing child restraints compared to forward-facing child restraints and boosters, and a 40% reduction in injury risk for children aged 2-4 using forward-facing harnessed restraints rather than boosters or seatbelts (Benedetti et al 2019).

A forward-facing child with shoulders held back by a harness during a significant frontal impact can experience severe loading of the cervical spine as the mass of head extends forward and is stopped by the neck. In a 48 km/h (30 mph) crash with a 25-g passenger compartment deceleration, for instance, the head of a forward-facing adult or child may experience as much as 60 or 70 g, because the occupant’s head stops later in the event and more abruptly than the vehicle’s floor pan. Even the strong neck muscles of military volunteers make little difference in outcomes in such an environment. Rather it is the skeletal strength of the vertebrae, in combination with the tightness of the connecting ligaments, that determines whether the spine will hold together and the spinal cord will remain intact within the confines of the vertebral column (Huelke et al. 1992, Stalnaker 1993). Adult cervical spines can withstand severe tensile forces associated with decelerations up to 100 g (McElhaney and Myers 1993) and failure is nearly always associated with vertebral fracture.

On the other hand, the immature vertebrae of young children consist of both bony segments and cartilage, and the ligaments are loose to accommodate growth (Kumaresan et al. 1998, Myers and Winkelstein 1995). This combination allows the soft vertebral elements to deform and separate under crash conditions, leaving the spinal cord as the only fragile link between the head and the torso. This flexibility allows children to sustain spinal cord injury without fracture to the vertebrae, which is extremely rare in adults. Mathematical models of pediatric spines (age 1, 3, and 6 years) subjected to various types of loading indicate that, compared to adult spines, the anatomical and material properties of immature spinal elements make them much more flexible than would be predicted by relative size alone (Kumaresan et al. 2000). Crash experience has shown that a young child’s skull can be separated from its spine by the force of a crash (Fuchs et al. 1989), the spinal cord can be severed (Hoy and Cole 1993) or the child may live but suffer paraplegia or quadriplegia due to the stretched and damaged cord (Langweider et al. 1990, Trosseille and Tarriere 1993, Weber et al. 1993). The risk of spinal cord injury in children increases with crash severity and decreases with age (Stalnaker 1993). Although serious cervical spine injuries are rare among properly restrained forward-facing children, because of the potentially severe consequences, best practice dictates the relatively simple countermeasure of restraining smaller children rear-facing as long as possible.

Tethers and crash performance

Top tethers should always be used with forward-facing child restraints to anchor the top of the child restraint to the vehicle and reduce forward rotation of the child restraint in a frontal crash (Brown et al. 1995, Legault et al. 1997). The video below compares the performance of the same model of child restraint tethered (closer to camera) and untethered (farther from camera) in a 48 km/h crash test with a 3-year-old sized dummy. The dummy in the child restraint attached with a tether experiences about 150 mm (6 inches) less forward movement of the head. Reduced head excursion means that in an actual crash, a child would be less likely to experience head contact with the interior. Among children injured in forward-facing child restraints, head and facial trauma predominate (Nance et al. 2010, Arbogast et al. 2002). Head contact while the neck is in tension can also generate vertebral fractures and dislocations, as well as spinal cord injury, by suddenly stopping the free motion of the head and putting significant compressive and shear loads on the neck (Stalnaker 1993, McElhaney and Myers 1993). Reduction of head excursion and elimination of head contact are therefore as important for avoiding neck injury as they are for reducing head and facial injury in children. Top tethers can also partially compensate for other misuses, such as loose installation using the LATCH strap or seatbelt (Manary et al. 2019) .However, the tether must be tight, as the improvement offered by a top tether is also degraded by slack. Failure to use the tether is a common misuse of forward-facing child restraints, occurring in half of forward-facing installations (Jermakian and Wells 2010).

Tether vs. no tether

Tether reducing effects of misuse

Forward-facing child restraints and side-impact protection

Although frontal impacts are the most common type of crash, side impacts are more likely to result in serious and fatal injuries (Viano and Parenteau 2008). Injuries to the head and face are most common in side impacts, so restraints with larger padded sidewings may offer some protection (Orzechowski et al. 2003, Arbogast et al. 2010, Maltese et al. 2007), but may be insufficient for keeping the head within the child restraint in the most severe crashes (Hauschild et al. 2015) Laboratory testing of child restraints with different types of LATCH hardware indicate that rigid LATCH offers improved protection by limiting motion towards the struck side of the vehicle (Klinich et al. 2005). Early tests using a tether and forward-facing child restraints showed a negligible effect on lateral head excursion compared to those without a tether (Klinich et al. 2005), while more recent work indicated that a tether could reduce lateral head excursion (Hauschild et al. 2016). Testing with additional energy absorbing elements (side air cushion) showed a significant improvement over a baseline design (Bendjallal et al. 2011). NHTSA has proposed side impact testing requirements for harnessed child restraint systems, but they are not yet required. Child restraint manufacturers may advertise that their products have been tested in side impact, but do not provide details on how they are doing so.

Forward-facing child restraints and airbags

Although all children are safer in the rear seat, if all of the rear seating positions are occupied, a child in a forward-facing harnessed child restraint would usually be the best candidate to ride in the right-front passenger position. A child well secured in a properly installed forward-facing child restraint should be at no greater risk of injury from airbag deployment than a belted adult in the same seating position. The use of a harness around the child reduces the likelihood of being out-of-position and thus close to an airbag than an older child in a booster seat or seatbelt. Of the children sustaining fatal injuries from deploying airbags, none was seated in a properly used forward-facing child restraint (NHTSA 2009). If a forward-facing child restraint needs to be installed in the right-front position, the vehicle seat should be positioned as far rearward as possible, while still allowing for accommodation of the rear seat occupant.