June 20, 2011
That an infant seat should be placed in the rear-seat of the car, facing rearwards is an article of faith, preached by the National Highway Traffic Safety Administration and the American Academy of Pediatricians. Manufacturers only make rear-facing infant seats.
On its website, NHTSA advises:
“A rear-facing car seat is the best seat for your young child to use. It has a harness and in a crash, cradles and moves with your child to reduce the stress to the child’s fragile neck and spinal cord. Your child under age 1 should always ride in a rear-facing car seat.”
But Transport Canada researcher Suzanne Tylko presented data at the biennial Enhanced Safety of Vehicles conference that questions the certainty of that policy. Transport Canada has been at the forefront of child motor vehicle crash safety research. In particular, the agency’s dynamic testing has yielded important insights. In this three-year study, TC tested 131 child restraints in 85 motor vehicle crash tests. The vast majority were rigid barrier tests on rear-facing infant seats, secured by a three-point belt conducted at speed of 48km/h; 11 were conducted at 56 km/h; and seven were conducted at 40 km/h. TC also tested seats in offset deformable barrier tests, conducted at 40 km/h. (Fourteen tests involved convertible seats installed facing the rear.)
The tests showed elevated head accelerations above 80g in 18 percent of the tests with a significant number occurring in the rear center seating position. There were four areas of impact: direct head contact with the rear seat back in front of the dummy; contact between the child restraint and the forward seat back; dummy head contact with the carry handle; and child seat with the center console between the front seats.
Transport Canada began to investigate the head protection offered by infant seats, when initial tests showed elevated head responses – some Head Injury Criterion values for the infant dummies, as high as 100g. Their observations have recently been buttressed by a May 2010 study by NHTSA’s National Center for Statistics and Analysis, citing head injuries as being the most common injury type for children in crashes. The study examined injuries to children ages seven and under, and found that the head was commonly injured region of the body, but infants under one year of age had a greater incidence of head injury than older children aged one to seven. Infants were more likely to have sustained a concussion or be rendered unconsciousness in a crash; 70 percent of children under 1 year old sustained AIS+2 head injuries.
The study pointed out that head injuries in children have long-range societal impacts:
“For example, children who suffer traumatic brain injuries can experience lasting or late-appearing neuropsychological problems, highlighting the need for careful monitoring of children as they grow older. For this reason, head injuries are of particular concern when studying children injured in motor vehicle traffic crashes. In children, some neurological deficits after head trauma may not manifest for many years. Frontal lobe functions, for example, develop relatively late in a child’s growth, so that injury to the frontal lobes may not become apparent until the child reaches adolescence when higher level reasoning develops. Since the frontal lobes control social interactions and interpersonal skills, early childhood brain damage may not manifest until such frontal lobe skills are called into play later in development. Likewise, injury to reading and writing centers in the brain may not become apparent until the child reaches school age and shows signs of delayed reading and writing skills.”
In three years of testing, Transport Canada confirmed their earlier findings. In several cases they saw the back of the infant seat slamming into the back of the front seat backs or the infant dummies ramping up their seat back, allowing the head to contact the back of the front seat backs, again, resulting in high HICs. In some instances, the carry handle interacted with the front seat back and broke off hitting the infant dummy in the head. The center position also revealed vulnerabilities – the back of infant seat and dummy head would hit the center console between the front two seats.
Larger infant seats slammed into the front seat backs harder. Researchers examined the effect of changing the clearance between the front seat back and the infant seat and found that with more clearance, there was more opportunity for the child to pick up speed, resulting in even higher HICs. With no clearance, as in most small cars, the seat is braced and had much better performance. Infant seats performed significantly better, if they were secured by universal anchorage systems, known in the U.S. as LATCH (Lower Anchors and Tethers for Children), because there was less excursion.
She took automakers to task for failing to install energy-absorbing seat backs. She criticized child restraint manufacturers for not installing energy absorbing padding on the infant seats, not even in the head area – only cover-over comfort foam over the hard plastic shell.
Tylko concluded: “The protection of an infant should be based on the same principles that are used to guide helmet design for head protection. The shell serves to distribute or spread the load over a large surface and the energy absorbing foam, crushes or deforms on impact to absorb the energy of the impact. To be effective, and reduce the risk of head injury, the foam must deform instead of the skull. If the foam is too stiff (high density) it will require too much energy to crush and the skull will deform. If the foam is too soft (low density) then the foam will bottom out and fail to absorb enough energy to prevent head injury. An impact test carried out with an instrumented head form or dummy can evaluate the effectiveness of the shell and foam liner combination by providing a measure of the amount of energy that is transmitted to the head during an impact.”
The real problem, however, is the lack of standards and dynamic testing, she said. The head injury criterion isn’t a very useful data point when the child seat is tested in a sled test, and there is no front seat back to provide the point of impact that would exist in a real-world crash. Tylko says that dynamic testing exposes hazards that would remain hidden in a sled test.
In lieu of standards, or industry initiative, Tylko says that the best advice for parents is not to place rear-facing infant seats in the center position and to use the LATCH system on either of the outboard seats.