In this research, the collision speed dependency of pedestrian head and chest injuries was investigated using the human FE model THUMS Version 4, independently developed by Toyota Motor Corporation and Toyota Central R&D Labs, Inc. to predict brain and internal organ injuries. In addition, this research also looked at the relationship between impact speed and fatality risk. The study first verified the biofidelity of the THUMS pedestrian model in terms of body region components, such as the head, chest, and lower extremities, and the whole body. The model closely simulated the impact response of each body region component described in the literature. As for the whole body kinematics, the calculated trajectories of each portion of the body during a collision with a vehicle were a good match with those of post mortem human subjects (PMHS) described in the literature. It was also determined that the model predicted injuries at the locations reported in the PMHS tests.

Using the validated THUMS model, this research then looked at the relationship of head and chest injuries with collision speed. Collisions between a pedestrian and an SUV were analyzed at three collision speeds of 30, 40, and 50 km/h. Head injuries did not occur at a collision speed of 30 km/h, but in collisions at 40 and 50 km/h the results suggested that a serious brain injury, known as diffuse axonal injury (DAI), occurred. Furthermore, in regard to the chest area, injuries did not occur at 30 km/h, but at 40 km/h bone fractures in the ribs occurred, and at 50 km/h, in addition to an increase in the number of bone fractures in the ribs, the results suggested that serious injuries to internal organs, such as damage to the heart, also occurred. These results correspond with the trends in accident data that indicate that the fatality risk for pedestrians increases when the collision speed is 40 km/h or higher.