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How Much Pedestrian Harm Can We Attribute to Larger Vehicles in the Fleet?

Project Description

This study will explore pedestrian injury outcomes in traffic collisions and the kinetic energy transfer from vehicles, contingent upon impact speed and weight. While research has shown that higher vehicle speed and size amplify the risk of fatal pedestrian injuries, limited attention has been given to the combined effect of vehicle design and speed on pedestrian fatalities. Although speculation links the increasing pedestrian fatalities in the United States to the growth of a vehicle fleet dominated by larger and heavier modes, particularly Sport Utility Vehicles (SUVs), our hypothesis diverges. We propose that at higher speeds, the significance of vehicle size diminishes in causing lethal pedestrian accidents.


This claim is supported by the kinetic energy transfer expression where speed is raised to the second power, thus overshadowing the role of vehicle weight. However, lower-speed pedestrian crashes might involve different dynamics, particularly in neighborhoods and parking lots. Collisions with SUVs could elevate the chances of fatality not only due to excessive size but also due to potential chest or abdomen impacts followed by running over, owing to their higher hoods and larger forward blind spots compared to sedans. Consequently, differentiating the thresholds for speed and vehicle size as determinants of pedestrian injury severity becomes difficult, with each scenario demanding distinct countermeasures.


Additionally, with the introduction of safety technologies such as pedestrian detection and emergency braking and increasing the trend towards vehicle electrification and automation leading to greater vehicle weight, understanding the extent of change in pedestrian injury risk is imperative. By employing econometric models, this study will utilize pedestrian crash and Vehicle Identification Number (VIN) data from California and Tennessee to investigate relationships among vehicle attributes, such as weight, speed, hood height, and safety features. For a more comprehensive understanding of these relationships, the study would also explore simulation techniques to model pedestrian-vehicle interaction during crashes involving different vehicle types, including SUVs and passenger cars.


The study will quantify the pedestrian harm from diverse vehicle sizes, spanning commercial vehicles, SUVs, and sedans, from other determinants of pedestrian injury severity using statistical models and a simulation approach. Specifically, the research will offer a novel contribution to identifying the threshold where a fatal pedestrian crash emerges through the complex interaction of vehicle speed and weight. Additionally, this research will explore the contribution of vehicle design, encompassing factors like hood height, blind spot characteristics, and related factors, which play a significant role in causing severe outcomes for pedestrians. Furthermore, the study's assessment of the effectiveness of vehicular safety technologies, including pedestrian detection and emergency braking systems, will bring forth valuable information about their role in mitigating severe pedestrian injuries. Lastly, the research will investigate potential future scenarios, examining the effects of the ongoing trend toward vehicle electrification and automation on pedestrian safety.


The potential outcomes of this study offer a hopeful prospect for enhancing pedestrian safety. This study will be based on the principles of the Safe Systems approach, emphasizing safer vehicles and speeds. With the potential irrelevance of vehicle size on roads with higher speeds, the study results will underscore the need for distinct countermeasures in high-speed and low-speed environments when considering the size or weight of the vehicle.


The study will also give insight into the importance of vehicle design elements that lead to severe pedestrian injury outcomes, enhancing our understanding of pedestrian-vehicle collision dynamics. These results would offer valuable guidance to transportation agencies like the National Highway Traffic Safety Administration (NHTSA) and the United States Department of Transportation (USDOT) for formulating vehicle design standards that prioritize safer interactions between pedestrians and vehicles, inlcuding innovative safety technologies such as pedestrian detection and autonomous emergency braking. Moreover, this investigation will also explore pedestrian safety within the context of an evolving vehicle landscape, such as considering the potential implications of an average increase in vehicle weights due to electrification and automation of vehicle fleets in the future.


Overall, the study's findings will enrich our understanding of pedestrian-vehicle collisions and help select appropriate safety measures.


06/01/2023 to 05/31/2024


University of Tennessee-Knoxville

Principal Investigator

Christopher Cherry
University of Tennessee-Knoxville
ORCID: 0000-0002-8835-4617

Research Project Funding

Federal: $71,638

Non-Federal: $25,731

Contract Number


Project Number


Research Priority

Promoting Safety

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