Seat Back Strength an Issue in Rear Seat Safety for Children

Researchers from the Center for Injury Research and Prevention at the Children's Hospital of Philadelphia looked at the effect of reported deformation of the front seat back rearward on the injury risk to children seated in the rear in a rear-impact crash.

Dr. Kristy Arbogast, Associate Director of Engineering for The Center for Injury Research and Prevention at CHOP, said that the study evolved from crash investigations conducted by their research team as part of several research projects. Researchers took note of several crashes in which a child seated in the rear of the vehicle suffered facial injuries in a rear-impact crash.

"We use real-world case studies to identify issues of interest and then move towards statistically-based inquiry. Is there an epidemiological basis? Are they isolated cases or indicative of a larger problem?" Dr. Arbogast said. "At first, we hypothesized that merely the presence of an adult in the front seat might be a factor."

CHOP examined cases from 2000-2006 of 1,035 restrained child occupants under 12 years old, seated in a second-row outboard position in rear crashes, and weighted the sample to represent 10,079 children. These data came from their Partners for Child Passenger Safety Study, a collaboration with State Farm Insurance.

The researchers analyzed the data to quantify the overall injury risk in relation to the presence of a front seat occupant and reported front seat-back deformation. Researchers found 2.3 percent of the children sustained an AIS 2+ injury; 71 percent of those crashes had a front seat occupant and 8 percent of the cases reported front seat-back deformation. For those children with reported seat-back deformation occurring directly in front of them, there was a doubling of the injury risk. The researchers, who presented the results of this survey at the 52nd AAAM Annual conference, provided the first population-based estimates of the injury risk of rear row-seated children in rear impact crash events. They concluded:

In the automotive safety community, the debate centers around mitigating injury for front seat occupants through design of the front seat, and little focus is placed on the role of seat back design on injuries to other occupants. Using two population-based samples, this study points to at least a two-fold increase in injury risk for children seated behind yielding seat backs in rear impact crashes, after adjusting for potential confounders such as crash severity.

Dr. Arbogast says that the study's results may be useful to automotive engineers striving to protect all vehicle occupants in a crash.

"What we were advocating for is to include the children as part of the equation as they are considering the front seat design," she said.

While the automotive safety community examines the consequences of inadequate seat-back strength to occupants, front and rear, NHTSA stands by. The agency has done virtually nothing to improve seat-back strength since it passed the Final Rule establishing Federal Motor Vehicle Safety Standard 207 in 1967. Its regulatory history is one of hesitation and contradiction, all the while acknowledging the need for improvement.

In the ensuing 40 years, the agency has tweaked the type of seats governed by the standard and extended its application to light trucks and buses. In 1974, NHTSA proposed merging seat back and head restraints (FMVSS 202) regulations under one safety standard, to reflect the critical relationship between these two elements of seating systems. Four years later, the agency nixed the idea, saying that it would explore new upgrades to head restraints and seat backs in the context of a more comprehensive occupant protection regulation.

In 1989, Dr. Kenneth J. Saczalski petitioned NHTSA to strengthen the requirements of FMVSS 207. A year later, seat and seat belt expert Alan Cantor petitioned the agency to amend FMVSS 207 to prohibit occupant "ramping" up the seat back during seat deformation. These petitions initiated a series of research efforts, beginning in 1992, when NHTSA launched a Seat Back Strength research project to gather information before moving forward with rulemaking activities. In its project summary, the agency acknowledged that the current standard was inadequate to insure that the seat does not fail when a car is subject to a severe rear impact.

Nonetheless, nothing changed, save for some announcements of intentions. In 2002, NHTSA published its rulemaking priorities for 2002-2005 and included improved seat strength and head restraints among its priorities, but proposed no new rulemaking. Two years later, NHTSA again signaled its intent to upgrade seat strength regulations in its fiscal budget. Then-NHTSA administrator Dr. Jeffery Runge listed the improvement of seating systems as one of three priorities for improving vehicle crashworthiness. But, again no new rulemaking materialized. In 2004, NHTSA published a notice terminating further rulemaking - even though one would be hard-pressed to determine exactly what was being terminated. The agency had made not a singe proposal to amend the rule in 12 years. And, everything old being new again, the agency said it would continue research with the goal of unifying FMVSS 202 and 207 into a single rear impact protection standard.

Meanwhile, CHOP researchers' conclusions add to the evidence that seat back strength is a critical factor in rear seat safety:

Seat back deformation may play a larger role in injury causation with younger children in child restraints who may be physically closer to the front seat back as it deforms. This suggests that seat back designs focused only on the front seat occupants may have unintended negative consequences for the rear seat occupants and points to consideration of both the front and rear seat occupants when evaluating trade-offs associated with seat designs.

Copyright © Safety Research & Strategies, Inc., 2009

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