Data from the Partners for Child Passenger Study shows that booster seat use among children ages 4-7 years has increased and its use is beneficial in terms of injury risk when compared to vehicle seat belts. However, results from sled tests with a 6-year-old Hybrid III ATD in four different high back booster seats (HBB) at a speed (56 km/h) higher than current compliance requirements (48 km/h) did not show corresponding benefits in some designs. Potential hypothesis for the apparent differences are 1) the lack of biofidelity of the ATD spine and neck 2) lack of high severity crash data from the field and 3) the possible differential performance of different HBB due to their design. A number of studies aimed at improving the biofidelity of the ATD have been done, but no study has looked at the differential performance of the HBB due to their design.

The study objective was to use mathematical models to investigate and assess the Hybrid III 6-year-old ATD performance due to the variation in seating angles of a HBB and seat belt positioning across the ATD. Mathematical models of the HBB and FMVSS 213 bench seat were developed using the multi-body MADYMO software. The standard MADYMO 6- year-old ATD model was used to assess the performance. This model was validated against a sled test and further parametric analyses were conducted. Parameters changed were the overall angle and the base angle of the HBB and the seat belt routing angle. The standard injury metrics (HIC, head and chest accelerations, Nij, and excursions) were used to quantify the ATD performance.

The study demonstrated that by optimizing the ATD seating posture and the belt positioning across its chest, improved ATD performance is achieved. An optimized angle of 5 degrees for base angle and 100 degrees for overall angle of the HBB, in combination with a belt angle of 40 degrees achieved better performance than the validated baseline model.