Recent studies suggest that there is increased risk to the pelvis and lower extremities for unbelted, front seat occupants when airbags deploy in frontal collisions. Among belted drivers, women and small adults are more likely to experience fractures of the knee-thigh-hip complex and lower leg. The occupant kinematics and impact mechanics for varying sized drivers under belted and unbelted conditions, with a deploying airbag, have not been well-investigated. The present study used occupant kinematic computer software (MADYMO) to investigate injury likelihood for the pelvis, femur and lower leg in simulations of FMVSS 208 test conditions (30 mph, rigid barrier, frontal crash) for a mid-size sedan with airbag deployment. The pelvic force criterion (PFC), femur force criterion (FFC), and Tibia index (TI) were calculated as injury predictors for 50th percentile male and 5th percentile female drivers, belted and unbelted, with variations in instrument panel angle and stiffness as well as hip abduction. The results indicated, most notably, that the unbelted 5th percentile female submarined beneath the airbag and experienced TI values that exceeded the current tolerance in nearly every unbelted simulation. Injury scores for the left leg were generally higher for both dummies, due to leg entrapment and the intruding floor pan. Hip abduction of 20 degrees led to excessive hip forces in the 50th percentile male. Seatbelts were effective at reducing injury measures in both dummies, most notably the TI score of the 5th percentile female.
Factors contributing to serious and fatal injuries in belted rear seat occupants in frontal crashes