No Love for LATCH

Another reason to ditch LATCH? A study recently published in Traffic Injury Prevention concluded that the Lower Anchors and Tethers for Children (LATCH) “does not offer equal protection to lap/shoulder belts from head injuries in rear impacts” when used with rear-facing infant safety seats.

The study, conducted by Robson Forensic, Inc., based in Lancaster, PA, tested three popular rear-facing infant child safety seats—the Graco SnugRide, the Britax Chaperone and the Evenflo Tribute --in rear-impact sled tests using three different installations – LATCH, and seat belts with Emergency Locking Retractors (ELR) and Automatic Locking Retractors (ALR). The safety seats were installed in the outboard seating positions of a sled buck representing the backseat of a 2012 Toyota Camry and occupied by a six-month-old CRABI dummy. The researchers were interested in how well LATCH secured the infant seat in comparison to seat-belt installations in a 30-mile-an-hour rear impact, given the physics of such a crash.

The study’s authors describe the kinematics of the RFCRS restrained with LATCH and the vehicle seatbelt in these tests:

The car and subsequently the lower anchors “move out from underneath” the RFCRS and child, forcing the attachment system to act as a fulcrum about which the RFCRS and child system rotates (Feles 1970). The weight of the infant contained within the RFCRS causes the center of mass of the car seat/child system to rotate about the attachment point. Restrained within the car seat with the available five point harness, the infant and the RFCRS have the ability to rotate and contact the seatback of the seat in which the RFCRS is installed. Due to the coupling of the RFCRS and child to the vehicle through the attachment system, whether by the available seatbelt or LATCH system, as the vehicle subsequently decelerates, the RFCRS rebounds off of the seatback while still attached either through the available seatbelt or LATCH system. Rotating and inverting the RFCRS in this manner could expose a properly restrained infant to head/neck accelerations not predicted by the vehicle dynamics alone. Thus, this could result in head contact with the seatback in which the RFCRS is installed, posing an additional risk of head trauma to the otherwise properly restrained infant.

High-speed videos in these rear-facing infant seat tests revealed very different kinematics from forward-facing child and adult restraints, namely the rotation of the seat and the dummy around its attachment axis, allowing the “child’s head to extend beyond the confines of the car seat in many instances, allowing the head to strike the seatback in which the RFCRS was installed. In tests of the Graco SnugRide® without the base it was observed the shell rotated in a manner that caused it to remain rotated in a near vertical orientation after the test was concluded…”

These effects were more pronounced in the LATCH configuration, resulting in an increase in angular momentum and rotation and more severe head strikes. The tests looked at Head Injury Criterion values, even though there are no Federal Motor Vehicle Safety HIC standards for a six-month-old infant. But, what is notable in this study is that the HIC values, which are based on acceleration, are much higher in Britax and Graco seats secured with LATCH -- 60 percent higher in the SnugRide and double in the Britax.)

The authors concluded: the results of this study suggest that LATCH does not offer equal protection to lap/shoulder belts from head injuries in rear impacts when used with infant seat type RFCRS.

The Saga of LATCH

Federal Motor Vehicle Safety Standard 213 required automakers to outfit their vehicles with LATCH by 2002 to address the problems of loose-fitting child safety seats, a common problem when seat belts are used to secure child seats. According to the Final Rule, LATCH would usher in the Golden Age of Rear Restraints:

This final rule will help vehicle and seat belt manufacturers design belts to more effectively perform a dual role. Manufacturers will be able to optimize seat belts to restrain older children, teenagers and adults. Further, the final rule will provide motorists with a means of securing child restraints that is easier and more effective. By requiring an independent child restraint anchorage system, the final rule improves the compatibility of vehicle seats and child restraints and the compatibility of seat belts and child restraints. Installation of the new system will result in more child restraints being correctly installed. The standardized vehicle anchorages and the means of attachment on child restraints are intuitive and easy-to-use. For example, they eliminate the need to route the vehicle belt through or around the child restraint. By making child restraints easier to install, correct use and effectiveness will be increased.

The agency was so sure that LATCH was the answer to the child safety seat mis-installation problem that it rescinded the seat belt lockability requirement beginning in September 2012, under the assumption that everyone would be using LATCH and not seat belts to secure child safety seats.

NHTSA’s enthusiasm was misplaced. First, widespread acceptance by parents and caregivers has been slow to come. The last published survey in 2006, showed that LATCH was frequently misused – when it was used at all. A survey conducted over six months in 2005 showed that significant percentages of parents misused LATCH – if they used it at all. NHTSA collected data on 1,121 children ages 4 and under, at 66 sites such as parking lots, health care centers, and recreation facilities in Arizona, Florida, Michigan, Missouri, North Carolina, Pennsylvania, and Washington. The observational study, Child Restraint Use Survey—LATCH Use and Misuse, revealed that 40 percent of parents continued to rely on seat belts; 13 percent of parents bypassed LATCH because they put their children in the center rear position, where there are no LATCH lower anchors. Of the 60 percent who did use LATCH, nearly half were using the lower anchors only and ignoring the upper tether and 13 percent were using the lower anchors in conjunction with the seat belt.  (These configurations can cause performance problems.)

Second, the agency eliminated LATCH for heavier and older children in 2003 when it significantly lowered the weight limit for the lower anchorages at the suggestion of the Alliance of Automobile Manufacturers, which opposed a NHTSA proposal that CRS be tested with a 10-year-old dummy, secured via LATCH. The Alliance argued that when NHTSA adopted the child restraint anchorage rule, the LATCH systems were intended for use by children up to 48 pounds. NHTSA agreed, allowing that when it revised the anchorage requirements in 2003 to accommodate the LATCH system, it had calculated the strength requirements on a combined weight of the child and CRS 65 lbs.

Child safety seat advocates observed that mixed messages to parents, weight limits, and other LATCH design gaps were to blame for its failure to dislodge seatbelts as a means of attaching child safety seats. For example, parents have been cautioned to place their child in the middle position of the rear seat, yet many vehicles do not have lower anchors for the center position. Manufacturers warn consumers against using the inner bars from the two outboard position anchors to secure a child safety seat in the center standard requires the lap belt to be lockable to tightly secure child restraint systems, without the need for locking clips attached to the seat belt webbing.

In 2012 NHTSA was forced to rescind its sunset clause of the lockability requirement.

As for NHTSA’s prediction that automakers, now relieved of their duty to child safety seats, throwing themselves into improving rear seat safety, it, too, has not come to pass -- a 2007 study of rear occupant safety in frontal crashes showed that “the real world data suggests that the fatality and serious injury risk in frontal crashes is higher for older occupants in rear seats than for those in front seats.” Other studies showed that in some models “the front seat position is more effective in reducing serious to fatal injuries for adult occupants in frontal crashes than the rear seat.”  

What Does This Study Tell Us?

This study suggests that if caregivers want to use the LATCH system with rear-facing infant seats, they should consider doing so with a tether. Tethers serve a critical purpose in reducing head excursion in a crash and few parents recognize its importance or that it can and should be used in conjunction with lower anchors or seat belts. The study’s authors refer to this type of installation in other countries, but apparently did not use tethers in their tests:

Swedish rear-facing child restraint designs differ from US products, in that they route a tether down and forward to a point on the floor in front of the vehicle seat where the CRS sits. This tethering system limits rotation towards the rear of the vehicle on rebound in frontal impacts or initial impact in rear impacts. The Australian method routes a tether rearward to the standard tether anchorage point used for forward-facing installations. By doing this, the forward rotation of the CRS is limited and allowed the child to “ride down” the collision with the vehicle.

Eight years ago, rear-facing infant seats in the U.S. did not have tethers. Today, a few brands, including Britax and Combi, include tethers in their rear-facing infant seat design.

The data on LATCH use and on rear seat safety is almost a decade old, so it’s difficult to know if LATCH has become more popular, driving automakers to make the rear seat a safer environment for adults. This study could be another indication that LATCH has yet a ways to go to fulfill its promise – or maybe it underscores the fact there are many facets to child safety seat performance – the vehicle seat geometry and seat-back design and the child restraint shell and harness design. One installation method can’t fit all.

And, beyond the vehicle seat-installation-child-safety-seat-system, this study emphasizes the failure of a regulatory system that allows manufacturers to design and sell products intended for every age of occupant, but can’t be used by families with children without special pieces of after-market equipment which caregivers must purchased and installed with no guidance from automakers.

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