Mathematical Simulation of Vehicle-Pedestrian Collisions: Influence of Vehicle Impact Speed and Front-End Structure on the Dynamic Responses of Child and Adult Pedestrians

Doctoral thesis, 2003

The development of effective countermeasures for pedestrian protection requires an understanding of how the impact speed and front-end design of the vehicle influence the injury risks of pedestrians. Because of the high involvement of children in pedestrian accidents, there is also a need for child pedestrian mathematical models. The objective of this study was to develop and evaluate child pedestrian MADYMO models and to improve the biofidelity of the existing adult models. Using these models, extensive parametric studies were carried out to evaluate the effects of various design parameters of vehicle front-end structure on the dynamic responses and injury risks of pedestrians. In the absence of biomechanical data of children, the child pedestrian models were developed by using scaling method. The validity of these child models was evaluated against real-world accidents. Reasonable correlations were achieved between the impact responses of the child models and the injury outcomes in accidents. For the validated adult models, bending and fracture joints were implemented in the lower extremity model in order to simulate the bending motion and multiple fractures of long bones. The results from the parametric studies indicate that vehicle impact speed has a significant effect on all injury-related parameters. The injury risk to the head, in terms of HIC and the head angular acceleration, could be significantly reduced as the impact speed decreases from 40 to 30 km/h. Other body regions could also benefit from a reduced impact speed. The kinematics and injury distribution of a pedestrian depend on the front shape of the striking vehicle, and can also be influenced by the stature of the pedestrian. Adults are exposed to high injury risks to the head, knee joint and, lower legs. Children sustain high impact loads to the head, chest, and pelvis. The head impact speed increases with a lowered hood edge. A pedestrian's head sustains both linear and rotational impact loads. The head angular acceleration is more appropriate for predicting the head injuries than HIC. The design parameters of the vehicle front structure could have different and even conflicting effect on the head rotational responses of child and adult pedestrians. It is therefore necessary to consider pedestrians of different stature to achieve an unbiased vehicle design. Nevertheless, increasing the energy absorption performance of vehicle front-end structure is likely to be effective in reducing the head injury risks to both child and adult pedestrians. The risks of long bone fractures and knee joint injuries are largely dependent on the characteristics of the bumper structure. The presence or absence of long bone fractures can significantly influence the impact responses of the knee joint. The results from this study suggest that an additional structure attached under the standard bumper with high energy absorbing capacity is likely to be effective in reducing the injury risks to the lower extremity. <> The child pedestrian models developed in this study are capable of predicting the dynamic responses and injury risks of children in vehicle collisions. The pedestrian mathematical models are valuable tools to develop effective countermeasures for the protection of pedestrians of different stature.