Objective:​ The objective was to determine the relative contribution of occupant versus child restraint system (CRS) kinematics to overall lateral head excursion for children in forward facing CRS (FFCRS) during oblique side impacts. As a secondary objective, the effect of the tether was investigated.

Methods and Data Sources:​ Sled tests were conducted with a FFCRS and Q3s Anthropomorphic Test Device (ATD) secured to a vehicle seat via LATCH, utilizing the center seat position. The vehicle seat and a simulated intruded door were secured to the sled at two angles (60 and 80 degrees from full frontal). Tests were conducted at 35 km/h delta-v, with and without a tether. Three-dimensional motion capture cameras captured kinematics of the ATD, FFCRS and vehicle seat. Head accelerations, neck forces and moments, and LATCH belt forces were obtained. The analysis focused on the relative contribution of the FFCRS motion versus the ATD motion with respect to the FFCRS on global lateral head excursion.

Results:​ The overall median lateral head excursion of the Q3s relative to the sled was 430 mm;​ approximately half of the excursion was the displacement of the head relative to the FFCRS (median 223 mm). Head angular motion relative to the FFCRS (median roll, pitch and yaw were -79, -55, and 34 degrees respectively) was greater than the overall angular motion of the CRS (median roll, pitch and yaw relative to the vehicle seat were -18, 5, and -17 degrees). Tether use influenced the FFCRS motion, but not the head motion within the FFCRS. Observations were similar across both test angles.

Discussion and Limitations:​ In order to gain a better understanding of side impact occupant protection for those restrained in FFCRS, this research examined both overall FFCRS motion as well as occupant motion within the FFCRS. Previous kinematic analyses typically examined only occupant motion relative to the vehicle frame of reference. A large proportion of the occupant’s lateral head excursion was due to the head movement relative to the FFCRS suggesting interventions that address both aspects of lateral kinematics – movement of the FFCRS as well as lateral bending/forward flexion of the occupant’s torso/neck relative to the FFCRS – might result in overall injury mitigation. It was important to note that while tether use reduced FFCRS motion, it did not significantly increase the motion of the head relative to the FFCRS due to increased restraint of the FFCRS. Limitations include testing one FFCRS, one delta-v, and FFCRS attachment with a flexible LATCH system.

Conclusion:​ Occupant lateral head excursion and angular kinematics in oblique side impact crashes are related both to movement of the FFCRS as well as significant motion of the occupant relative to the FFCRS. This finding suggests two pathways for design intervention to mitigate overall occupant lateral excursion and potential impact with intruding structures, a common injury causation scenario for children in these crashes.