Investigation of Head Injuries in Car-to-Child Pedestrian Accidents

Licentiate thesis, 2006

Head injury is the most common injury type in child pedestrian accidents and could lead to lifelong disability or even death. To protect child pedestrian from head injury, it is important to understand the head injury mechanisms and tolerance levels. However, due to the lack of biomechanical data of child pedestrian, little progress has been made in this area. This study thus aimed at investigating head injury mechanism in child pedestrian accident by in-depth accident analysis and accident reconstructions. In paper I, a child pedestrian accident case was reconstructed based on the detailed information about the occurrence of the accident, victim injuries, vehicle damage, and accident environment. Child headform impact tests were carried out to acquire the force-deformation characteristics at the head and hip impact locations of the accident car. A facet child pedestrian model was developed by using scaling method. This facet model and a multibody system (MBS) child pedestrian model were used for the accident reconstruction respectively. The reconstructed pedestrian kinematics corresponded well with the measured accident data in terms of wrap around distance and throw distance. The head impact conditions were identified which included head impact velocity, impact angle, and head contact timing. Head injury parameters including 3 ms acceleration, HIC15 value, angular velocity and angular acceleration were calculated and correlated with injury outcomes in the accident. The results showed by correlating the calculated injury parameters with the injury outcomes in the accident, it is possible to evaluate the current injury criteria and threshold for child pedestrian, which is scaled down from adult data. Both MBS and facet child pedestrian models could replicate pedestrian kinematics in the accident although minor difference existed. In paper II, an in-depth accident analysis was carried out based on 23 child pedestrian accident cases from GIDAS database. These accident cases were reconstructed using MADYMO program with mathematical passenger car and child pedestrian models developed at Chalmers University. The EEVC pedestrian component test results were used to derive the corresponding stiffness corridor of the car front. The accident analysis proved that the head was the most frequently and severely injured body part. Most child pedestrian accidents occurred at impact speed lower than 40 km/h and 98% of the child pedestrians were impacted from the lateral direction. The child initial posture at the moment of impact was identified. 47% of children were running which is remarkable compared with the situation of adult pedestrians. From accident reconstructions it was found that the head impact conditions and injury severities were dependent on the shape and stiffness of the car front, impact velocity and the anthropometry of the children. The head injury criteria and tolerance levels were analyzed and discussed by correlating the calculated injury parameters with injury outcomes in the accidents. The results indicated that reducing the head injury should be set as a priority in the protection of child pedestrian. HIC is an important criterion of child pedestrian head injury and its injury tolerance could have a large variation due to personal differences. By limiting the vehicle speed and improving car front design, the head injury severity of child pedestrian could be reduced.