Can new passenger cars reduce pedestrian lower extremity injury? A review of geometrical changes of front-end design before and after regulatory efforts

ABSTRACT

Objective: Pedestrian lower extremity represents the most frequently injured body region in car-to-pedestrian accidents. The European Directive concerning pedestrian safety was established in 2003 for evaluating pedestrian protection performance of car models. However, design changes have not been quantified since then. The goal of this study was to investigate front-end profiles of representative passenger car models and the potential influence on pedestrian lower extremity injury risk.

Methods: The front-end styling of sedans and sport utility vehicles (SUV) released from 2008 to 2011 was characterized by the geometrical parameters related to pedestrian safety and compared to representative car models before 2003. The influence of geometrical design change on the resultant risk of injury to pedestrian lower extremity—that is, knee ligament rupture and long bone fracture—was estimated by a previously developed assessment tool assuming identical structural stiffness. Based on response surface generated from simulation results of a human body model (HBM), the tool provided kinematic and kinetic responses of pedestrian lower extremity resulted from a given car's front-end design.

Results: Newer passenger cars exhibited a “flatter” front-end design. The median value of the sedan models provided 87.5 mm less bottom depth, and the SUV models exhibited 94.7 mm less bottom depth. In the lateral impact configuration similar to that in the regulatory test methods, these geometrical changes tend to reduce the injury risk of human knee ligament rupture by 36.6 and 39.6% based on computational approximation. The geometrical changes did not significantly influence the long bone fracture risk.

Conclusions: The present study reviewed the geometrical changes in car front-ends along with regulatory concerns regarding pedestrian safety. A preliminary quantitative benefit of the lower extremity injury reduction was estimated based on these geometrical features. Further investigation is recommended on the structural changes and inclusion of more accident scenarios.

KEYWORDS:

• pedestrian safety
• car front-end design
• regulatory efforts
• finite element human body model
• lower extremity injury
• injury biomechanics

Acknowledgments

The authors acknowledge Dr. Bing Deng and Dr. Mark Neal at General Motors for their contribution to the construction of this study. We appreciate Zheng Shen, Yan Meng, Peijun Ji, and Xinjiang Xiang, who were or are students at Tsinghua University, for their contribution in the survey of car models. Additionally, we acknowledge Dr. Jason Kerrigan and Dr. Taewung Kim at the University of Virginia for their insightful comments and suggestions. The opinions expressed here are solely those of the authors.