Influence of non-standard seating postures on safety of motorcoach passengers in frontal collisions: A numerical study

•Motorcoach sled tests are simulated numerically with stochastic occupant postures.•Posture significantly affects the safety of unbelted passengers in frontal collisions.•HIC values can be increased by a factor of two from a standard posture.•No direct correlation between posture parameters and injury criteria is observed. With increasing public concern about the safety of motorcoach passengers, new regulations have been established for large passenger vehicles worldwide. In contrast to regulation testing, the real-world environment features several uncertainties that can potentially increase the injury risk for occupants. This paper is aimed at investigating the effect of the non-standard occupant seating posture, stature and low seatbelt usage rate on the safety of motorcoach passengers in frontal collisions. The study is performed numerically, using the validated finite element model of a sled test. The posture of the two unbelted occupants, 5th and 95th percentile ATDs, is varied stochastically according to the results of a volunteer study available in the literature. Compared to the reference posture used in the regulation testing, a maximum variation of +104% is observed for the Head Injury Criterion (HIC) and +58% for the femur forces of the 95th percentile ATD. The HIC and femur forces for the 5th percentile ATD and neck injury criteria for both ATDs demonstrate a difference of about 20% from the standard posture. No direct correlation is observed between posture parameters and the probability of an injury. Overall, the results of the study provide an estimate of the dispersion in the injury criteria values introduced by posture variations and highlight the importance of accounting for the real-world uncertainties during design and testing of vehicle structures.