The introduction of automated driving systems (ADS) is likely to change the very nature of personal transportation. Without the need to drive, occupants will have more freedom to engage in other activities, which could result in major changes to vehicle interiors, controls, and seating configurations. Reclined posture seating may be an option that manufacturers consider in the relatively near term. The goal of this study is to evaluate how varying occupant anthropometry, distance to the knee bolster, and seatback angle affect occupant response.

A finite element model of a vehicle occupant compartment with the state-of-the-art seatback integrated restraint system was used, to evaluate three different simplified Global Human Body Model Consortium (GHBMC) occupant models (small female, midsize and large male) in frontal crashes. A full factorial sensitivity study was performed with four different levels of seatback recline (0, 10, 20, 30 deg) and four different distances to the instrument panel knee bolster resulting in total of 40 simulations.

Increasing the seatback recline angle caused the occupants’ pelvis to submarine under the lap belt, which, in turn, resulted in poor pelvis-belt engagement and increased occupant excursion. Larger occupants tended to be able to withstand higher seatback recline angles without submarining than smaller occupants. Additionally, across all occupants, increased recline angle resulted in increased lumbar compression and shear force.

The new ADS environment is likely to pose substantial challenges to occupant restraints systems. Increased seatback angle increases the propensity of occupants to submarine, and results in increased lumbar spine load.