Evaluation of Rotation Reduction Features in Infant and Extended-Use Convertible Child Restraint Systems during Frontal and Rear Impacts.

A correctly used child restraint system (CRS) is associated with a substantial reduction of injury and mortality risks in motor vehicle crashes and epidemiologic data suggests that toddlers are provided greater protection when restrained in a rearward-facing CRS compared to a forward-facing CRS. Some 'extended-use' European CRS models can accommodate children up to six years rearward-facing and have a support (load) leg and/or a pair of lower (Swedish) tethers to reduce rotation during frontal and rear impacts, respectively. Laboratory studies have found that a support leg reduces head and neck injury metrics of anthropomorphic test devices (ATDs) younger than three years in rearward-facing CRS models during frontal impacts. The objectives of the current study were to perform sled tests to: (1) evaluate the effects of using a support leg in rearward-facing infant and extended-use convertible CRS models during frontal impacts, (2) evaluate the effects of using a pair of lower tethers in a rearward-facing extended-use convertible CRS model during rear impacts and (3) compare responses of ATDs in an extendeduse convertible CRS with a support leg and a pair of lower tethers in rearward- and forward-facing configurations during frontal and rear impacts. The presence of a support leg in rearward-facing infant and extended-use convertible CRS models in frontal impacts was associated with reductions in head injury metrics across a range of pediatric ATDs and neck injury metrics were below injury tolerance values. Other strategies in the design of rearward-facing CRS and front row vehicle seatbacks may be available to further reduce head injury metrics. Lower tethers reduced the rearward rotation of an extended-use convertible CRS toward the vehicle seatback in rear impacts and were typically associated with reductions in head and neck injury metrics for the Q6 ATD, but not the Q3 ATD. For frontal impacts, neck injury metrics were typically greater for ATDs in the forward-facing extended-use convertible CRS, whereas head injury metrics were typically greater for the rearward-facing condition (with a support leg and a pair of lower tethers). Interactions of the ATD head and/or the rearward-facing extended-use convertible CRS with the blocker plate in rearward-facing frontal impacts need to be further investigated.