Analysis of kinematic behavior of pedestrians/cyclists in vehicle collisions using impulse.

Objective: In order to further reduce the injury risks to pedestrians/cyclists in vehicle collisions, it is necessary to control pedestrian/cyclist kinematics. To investigate pedestrian/cyclist kinematic behavior from initial contact with the vehicle to the ground contact, it is necessary to evaluate the force interactions between the pedestrian/cyclist body region and the car body during the crash event.Method: Finite element analysis was conducted for models of pedestrians and cyclists being struck by a car around the center, left, and right sides of the front of the vehicle at 40 km/h. The impulse that was applied to each body region of the pedestrian/cyclist by the vehicle body during the impact was employed to analyze the kinematic behavior of the pedestrian/cyclist.Results: An impulse-time history can be separated into three stages. In the first stage, the pedestrian/cyclist was accelerated by the vehicle's forward impulse imparted to the subject due to the lower extremities contacting the bumper and hood leading edge. In the second stage, the pedestrian/cyclist rotates around the hood leading edge. In the third stage, the pedestrian/cyclist was accelerated in the vehicle forward and upward directions by the impulse resulting from the contact of the head and upper extremities with the cowl and the windshield. As the impulse to the lower extremity increased, the wraparound distance (WAD) decreased; however, the pelvis velocity in the forward direction increased.Conclusion: This research employed a new approach using the impulse transmitted to each body region due to contact with the vehicle body and showed that impulse is a useful parameter to understand the process of pedestrian/cyclist kinematics. The impulse relates to the linear and angular velocities of the pedestrian/cyclist at the time of separation from the car, thereby providing useful information to control pedestrian/cyclist falling kinematics prior to the ground impact.