Investigation of factors influencing submarining mitigation with child booster seats.

OBJECTIVE: Automobile booster seats are intended to improve belt fit for children that are too large for a harness-style child restraint, but not yet big enough to fit properly in an adult seat belt. Our objective was to prospectively study the relationship between booster seat design and interaction with the seat belt (specifically, submarining risk) for a child occupant using computer simulation of automobile crash events. METHODS: Frontal-impact simulations were performed with a 6-year-old child human body model. Simplified models of booster seats were developed using an automated process designed to capture key characteristics of booster geometry, stiffness, belt guide construction, and attachment to the vehicle seat. The child model was positioned in a range of postures from upright to slouched. Our main interest was submarining, where the child's pelvis slips under the lap belt and the belt loads into the abdomen (defined based on the motion of the lower lap belt edge relative to the ASIS). RESULTS: Among the parameters studied, the factors that had the greatest effect on submarining risk were the booster's stiffness and the child's posture. Booster models of a low-stiffness construction (similar to an inflatable booster) nearly always resulted in submarining, regardless of the other design characteristics of the booster. A slouched posture also substantially increased the likelihood of submarining (even for high-stiffness boosters). CONCLUSIONS: These results suggest that booster seats of a stiffer construction, and booster seats that promote an upright posture may provide a protective benefit compared to softer boosters and boosters that are more likely to result in slouching of the child.

IIHS head restraint ratings and insurance injury claim rates.

OBJECTIVES: The Insurance Institute for Highway Safety (IIHS) rates front seat/head restraint designs using a combination of static and dynamic measurements following RCAR-IIWPG procedures. The purpose of this study was to determine whether vehicles with better IIHS-rated seats/head restraints had lower injury risk in rear-end collisions and how the effect of better rated seats interacted with driver gender and age. METHODS: The presence of an associated insurance injury claim was determined for rear-impact crashes using 2001-2014 model year cars and SUVs. Logistic regression was used to compare injury risk for vehicles with good, acceptable, and marginal IIHS-rated seats/head restraints with poor-rated seats/head restraints. Analyses were run by gender and driver age and also by the rate of more severe injury claims. RESULTS: Injury rates were 11.2% lower for vehicles with seats/head restraints rated good compared to vehicles with seats/head restraints rated poor. The percentage reduction for good- versus poor-rated seats was greater for females (12.7%) than males (8.9%). Comparing good- with poor-rated seats, driver ages 15-24 had the largest reduction at 19.8%, followed by 10.7% for driver ages 45-64 and 10.4% for driver ages 25-44. CONCLUSIONS: Seats/head restraints with better IIHS ratings are associated with lower injury rates in rear-impact collisions than seats rated poor. The reductions in injury rates were strongest for females and for young-to-middle-age drivers. The strong reductions in injury rates for these groups are encouraging given their high initial injury rates.