Call to Industry and Government: Bring Rear-Seat Safety to Its Full Potential

This article originated in the May/June 2013 issue of Safe Ride News.

Although it is always safer to ride in a vehicle’s back seat, the relative benefits today decline for children as they age, particularly after they have transitioned out of a CR. This is the overall finding of a Center for Injury Research and Prevention (CIRP) study of the state of science on the safety of children and youth in the rear seats of vehicles. CIRP, a group that is part of The Children’s Hospital of Philadelphia, published the findings in its April 2013 CPS Issue Report.   “Optimizing the Rear Seat for Children” includes extensive review of the scientific literature relevant to this subject since 2001.

The CIRP notes that children are the primary occupants of rear vehicle seats, with children less than 14 years old comprising 70 percent of all such occupants. The study suggests that rear-seat safety technology has not kept pace with the times, since today’s children ride in vehicles nearly as much as adults do—averaging 3.4 trips and up to 50 minutes per day.  Rear vehicle occupant spaces that acknowledge this trend through child-friendly safety features would be the ideal, but are, in actuality, far from the norm.

Looking at Partners for Child Passenger Safety data from 2007, the report found that injury risk increases as children age: for children 0-3 years old, there are 4.5 injuries per 1,000 children, but the injuries increase to 7.0 for children 4 to 8 years, 15.5 for children 9 to 12 years, and 20.6 for 13 to 15 years.  It cites strong safety benefits for all children restrained in a CR, with only 4 injuries per 1,000 children, and for those in boosters, with 5.5 injuries per 1,000.  Various studies indicate a benefit to riding in the rear, showing an elevated risk of injury of anywhere from 40 to 70 percent when children are instead seated in the front seat; also, the types of injuries of front-seated children are more severe.

However, the data show that rear-seat benefits decline after age 13—and more so in recent years. The study concluded that the shrinking difference between safety in the front and rear seats over the past decade has more to do with improvements to the safety of front-seated passengers than increased dangers of riding in the rear. To see similar improvements to safety in the rear, one recommendation the authors make to regulators and industry is to consider adapting for the rear the types of technology that has augmented the front seats of today’s vehicles. For instance, seat belt load-limiters and pretensioners could be made more available in rear seats, as well as side-impact air bags.

The researchers note, however, that any new technology must be carefully assessed and amended, as necessary, for appropriateness for children (and also the elderly). Load-limiters, which add slack to a belt when an amount of force that can induce injury is detected, protect the chest but allow more head excursion. Pretensioners, which quickly take slack out of a belt when rapid deceleration is detected, do the opposite—they can decrease head excursion (and submarining), but the sudden tightening could cause chest injuries. Technologies that can offset these concerns in the front seat, such as frontal air bags and knee bolsters, aren’t available to supplement these features in the rear.

Computer modeling, however, suggests that these seat belt technologies in the rear could substantially reduce the risk of the most serious injuries, especially when used together. Sled testing also demonstrates the benefits of side-impact torso air bags, as well as side-curtain bags, which are especially protective in rollover crashes.

Another observation is that current rear-seating geometry—the size and shape of the seating and seat belt anchorage—is rarely optimized for children (or even many adults). A study of seat cushion depth found that most vehicles are much bigger than needed for optimal restraint and comfort. The median second-row seat cushion depth of 17.9 inches (455 mm) is longer than the thigh length of 83 percent of children and 24 percent of adults. This causes occupants to slouch so that the knees can bend comfortably, which allows the lap belt to slide up onto the abdomen and the shoulder belt to ride too high. Another observation is that only 35 to 55 percent of shoulder belts can be adjusted to fit across the mid-clavicle of average-size children ages 8 to 15. The report suggests that vehicle designers take a lesson from booster seat design to inform how proper placement of belts can be achieved and also how better fit could improve behavior so belts remain in place.

The report concludes that, despite the fact that great strides have been made over the past decade to protect children in vehicles, nearly a thousand children die each year in car crashes, and much can still be done to further reduce these tragedies. Recommendations to government and industry include further research on injury mechanisms and occupant behaviors, more customizable occupant protection designs, and improvements to interventions, regulations, and laws for the protection of older children.

Optimizing Features for All Occupants

Ford Inflatable Seat BeltThe CIRP’s report focuses on adding features that enhance safety for older children in the rear seats of vehicles, and it notes that any child riding in a CR or booster is the most protected. SRN editors add that, along with the research that must be done to carry out the report’s recommendations, effort must be made to determine how such changes can be made to be compatible with CR installation and use. For example, as noted in the CIRP study, one of the few examples of rear-seat-specific technology is Ford’s inflatable seat belt air bags, available as an option in select models since 2011. Although such efforts should generally be applauded, a great deal of coordination between the CR and vehicle industry has been necessary to determine the safety of using this technology with CRs, an effort that is ongoing.

An Inherent Challenge: Biomechanics Differ With Age

One of the toughest challenges facing regulators and automakers is that passenger biomechanics differ with age. As explained in the CIRP study, an elderly adult’s reaction to crash forces—and occupant protection technology—is far different than either an average adult’s or child’s. Creating technology that can adapt to meet the needs of all occupants must be the focus of future design. Even among children, the biomechanics vary greatly:

Children 13 years and older:

Children in this age group tend to respond to frontal crashes like adults. Among restrained passengers in this age group, 76 percent of injuries are to the thorax (chest) region, with 95 percent of those injuries attributable to the seat belt.

Children younger than 13:

Head injuries are much more likely among younger children in frontal crashes. The researchers suggest this has to do with biomechanical differences between children and adults that make it more likely that children’s heads will strike the vehicle interior.