Pedestrian protection research at the University of Virginia: an Overview
Description
Pedestrian crashes present a universal challenge for public health, trauma medicine, and traffic safety professionals. Approximately 760,000 (65%) of the 1.17 million people that die as a result of road traffic accidents every year are pedestrians [1]. Relative to occupants involved in accidents, pedestrians sustain more multi-system injuries with concomitant higher injury severity scores and mortality rates [2]. Studies in the United Kingdom have shown that the average societal cost and fatality rate of pedestrian casualties are both approximately twice the corresponding numbers for vehicle occupant casualties [3,4].
Despite the aforementioned statistics, automotive safety research has traditionally focused on developing knowledge, systems, and devices for protecting vehicle occupants. The lack of effort devoted to countermeasures for pedestrian safety has stemmed primarily from a societal view that the injury caused by a large, rigid automobile striking a small, fragile pedestrian cannot be significantly reduced by alterations to the vehicle structure. Automotive safety engineers, however, have long been aware that the same safety design principles that have resulted in enormous benefits for occupants can be extended to make cars less aggressive to pedestrians.
The primary goal of the pedestrian protection group at the University of Virginia Center for Applied Biomechanics (UVA-CAB) is to perform research that aids in the development of vehicle designs that are less harmful to pedestrians. Current research activities include identification of the most common real-world pedestrian crash scenarios, characterization of human body response and injury thresholds in the pedestrian loading environment and development of computational and experimental tools for evaluating the effectiveness of vehicle design concepts for pedestrian protection, and development of age dependent injury criteria for pediatric pedestrians.
Real-World Crash Investigation
The pedestrian protection group provides biomechanical engineering input to the Crash Injury Research and Engineering Network (CIREN). CIREN is a multi-center research collaboration of clinicians and engineers in academia, industry and government, which aims to improve the understanding of the complex mechanisms of automobile crash injuries by in-depth investigation of real-world crashes. UVA-CAB provides biomechanical engineering input to the Honda-Inova Fairfax CIREN center, which is the only CIREN center that investigates pedestrian accidents. For selected cases in the CIREN database, UVA-CAB also conducts in-depth accident reconstruction investigations using iterative computational modeling.
Response and Injury Thresholds in the Pedestrian Impact Loading Environment
Characterization of the response and injury thresholds of the human body in the pedestrian impact loading environment is necessary for the purpose of obtaining validation data for physical and computational models that need to be able to mimic human response in simulations of pedestrian accidents. Due to the high frequency of lower limb injuries seen in pedestrian casualties, UVA-CAB focuses on characterizing the response and injury thresholds of the lower limb long bones, the knee joint and the cruciate and collateral ligaments of the knee joint. Using human cadaveric specimens, UVA-CAB is performing experiments that seek to load the femur and the tibia-fibula complex in dynamic lateral bending; the knee joint in dynamic valgus bending and shearing, and the collateral and cruciate knee ligaments in dynamic tension to failure. In addition, UVA-CAB is in the process of preparing for full scale-pedestrian impact sled tests with testing anticipated in the spring of 2004.
Development of Computational and Experimental Tools:
• Human Finite Element Model for Pedestrian Impact Simulations
UVA-CAB is currently in the process of developing a full-body finite element (FE) model of the adult 50th-percentile standing male for use in the pedestrian impact loading environment. The model consists of an FE representation of the lower extremities that is currently under development at UVA, existing FE descriptions of the head and thorax, and multi-body descriptions of the remaining body segments. The lower limb mesh, which includes detailed descriptions of the long bones, flesh, knee ligaments and articulating geometry, was developed from data from the Visible Human Project and scaled to match the anthropometry of a 50th-percentile adult male. Tissue material properties are obtained from literature and from in-house testing. Segment validation for the long bones and the knee joint is carried out by simulating the experiments with human cadaveric specimens discussed above. The full-body finite element model will be validated against the results from full-scale pedestrian impact sled tests.
• Anthropomorphic Test Devices (mechanical legform impactors)
UVA-CAB has performed initial investigations to examine the biofidelity of the majority of the currently available legform impactors, including the TRL impactor recommended by the EEVC (European Enhanced Vehicle-Safety Committee) Working Group 17, the flexible legform impactor (FlexPLI) developed by JARI (Japan Automobile Research Institute) and the lower extremity of the Polar-II dummy developed by Honda Motor Company. These investigations typically included replicating the loading environment used in the aforementioned tests with human cadaveric specimens and comparing the results to the data from the cadaveric tests.
References:
1. World Bank (2001) Road Safety. http://www.worldbank.org/transport/roads/safety.htm
2. Brainard, B. J., Slauterbeck, J., Benjamin, J. B., Hagaman, R. M., Higie, S. (1989) Injury Profiles in Pedestrian Motor Vehicle Trauma. Annals of Emergency Medicine 18(8), pp. 881-883.
3. Factsheet: Pedestrian Casualties in Road Accidents: Great Britain 1998. Department of the Environment, Transport and the Regions.
4. Highways Economics Note No.1: 2000. Road safety. Department of Transport, Local Government and the Regions.