Comparative Analysis on Traumatic Brain Injury Risk due to Primary and Secondary Impacts in a Vehicle-Pedestrian Sideswipe Accident

A series of vehicle-to-pedestrian sideswipe impacts were computationally reconstructed; a fast-walking pedestrian was collided laterally with the side of a moving vehicle at 25 or 40 km/h, which resulted in rotating the pedestrian’s body axially. Because of a limited interaction between the human body and striking vehicle, the struck pedestrian was projected transversely from the vehicle and fell to the ground close to the first impact point. Potential severity of traumatic brain injury (TBI) was assessed using linear and rotational acceleration pulses applied to the head and by measuring intracranial brain tissue deformation. We found that TBI risk due to a secondary head strike with the ground can be much greater than that due to a primary head strike with the vehicle. Further, an ‘effective’ head mass, m_eff, was computed based upon the impulse and velocity change involved in the secondary head strike, which mostly exceeded the mass of the adult head-form impactor (4.5 kg) commonly used for a current regulatory impact test for pedestrian safety assessment. Our results suggest that TBI risk due to a ground impact would be mitigated by actively controlling m_eff, because m_eff is closely associated with a pedestrian’s landing style in the final event of ground contact.