Occupant Dynamics During Crash Avoidance Maneuvers

Abstract

A test-track study was conducted to assess the effects of initial posture and position on the head motions of front-seat passengers in abrupt vehicle maneuvers. A pilot study with 12 participants was conducted in a sedan, a minivan, and a pickup truck to assess whether head excursions differed across vehicles. Each participant experienced two abrupt braking events, two lane changes, and turn-and-brake maneuvers. Peak vehicle accelerations were about 1 g and 0.7 g in the braking and lane-change events, respectively. Head position was tracked using a custom, semi-automated system that uses a single depth camera. Head center of gravity (CG) location was estimated from landmarks identified on a three-dimensional scan of the participant’s head and face. Forward head excursion was slightly smaller in the passenger car than in the other two vehicles. No explanation for this finding was apparent; the vehicle kinematics were similar. A larger study was then conducted using a passenger sedan and an SUV. A total of 90 men and women with a wide range of age and body size were assigned to test-condition blocks that addressed a variety of initial conditions. The factors investigated were seat position, foot placement, seat back recline angle, retractor locking, vehicle differences, and the effects of leaning inboard on the console armrest or leaning forward while reaching. Each participant experienced two braking events, a right-going lane change, a left-going lane change, and a turn-and-brake maneuver. The two vehicles performed similarly, and the acceleration profiles were similar to both the pilot study and a 2018 study at the same facility. Greater forward head excursion relative to the seat was observed when the seat was further rearward or reclined, or the feet were placed flat rather than resting on the heels. No difference in forward excursion was noted across vehicles. Forward leaning reduced forward head excursion during braking events, but the head position was more forward than when starting from a standard posture. Younger participants exhibited slightly larger forward excursions, but overall anthropometric effects were small. Forward lean produced much larger lateral excursions than the standard posture. Recline reduced lateral excursions, as did resting the feet on the heels rather than flat on the soles. Greater outboard excursion was observed in the SUV during the left lane change, possibly because greater space was available than in the sedan. Higher BMI and younger age were associated with slightly larger lateral excursions in some conditions, but anthropometric effects were small compared with the effects of test conditions. A functional regression analysis of head CG trajectories on the primary axes of motion was conducted. The results provide insight into the effects of test and occupant variables on head motion. Parametric corridors were developed that can be used to tune and validate computational models of occupant responses in pre-crash maneuvers. Overall, the results suggest that a wide range of occupant head locations can be produced by abrupt vehicle maneuvers. More research is needed to assess the robustness of occupant protection systems to this wide range of postures.