The Influence of out-of-Position Displacement during Emergency Braking on Occupant Whiplash Injury in Subsequent Rear-End Collisions

In the pre-crash emergency braking scenario, the occupant inside the vehicle will move forward due to inertia, deviating from the standard upright seating position for which conventional restraint systems are designed. Previous studies have mainly focused on the influence of out-of-position (OOP) displacement on occupant injuries in frontal collisions, and provided solutions such as active pretensioning seatbelts (APS). But little attention has been paid to the influence of OOP on whiplash injury during a subsequent rear-end collision. To investigate the forward OOP impact on whiplash injuries and the effectiveness of APS in this accident scenario, a vehicle interior model with an active human body model (AHBM) was setup in the MADYMO simulation platform. Different braking strengths (0.8g and 1.1g), APS triggering times (from 0.2s before to 0.2s after the braking initiation) and pretensioning forces (from 100N to 600N) were input to the simulation matrix. The occupant’s forward OOP displacement prior to the rear-end collision and the corresponding whiplash injury metrics including neck shear force, tension force, and neck injury criteria (NIC) in the subsequent moderate rear-end collision were recorded. The simulation results indicated that: (1) The occupant’s whiplash injury metrics were positively linearly correlated with the pre-crash forward OOP displacement. (2) The APS could not fully eliminate the forward displacement brought by neck flexion, causing whiplash injury metrics to exceed the capping limits (upper bounds) defined in current vehicle safety assessment protocols like Euro-NCAP.