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Another study relates taller vehicle front ends to more pedestrian deaths

Suggest a maximum 49-inch hood height would save 509 lives per year


Car wreck

Pedestrian deaths hit a modern low in 2009. One of the side effects of the rampaging popularity of ever-larger vehicles since then: Studies examining the correlation between pedestrian deaths and ever-larger vehicles. The question of correlation didn't begin in 2009; here's a study from 2008. Questions of correlation and causality seemed to pick up in the news cycle around 2018, when final numbers from the National Highway Traffic Safety Association put pedestrian deaths in 2016 at their highest level since 1990. In 2018, NPR reported, "A new study by the Insurance Institute for Highway Safety found that between 2009 and 2016, pedestrian fatalities increased in nearly every circumstance examined. But among all types of vehicles, SUVs had the biggest spike in single-vehicle fatal pedestrian crashes, and crashes were increasingly likely to involve high-horsepower vehicles." So began regular bouts of stories like, "Death on foot: America's love of SUVs is killing pedestrians," of politicians asking for pedestrian safety ratings on certain vehicles, more studies like, "Pedestrian deaths and large vehicles," and more opinion pieces like, "The Troubling Tie Between Big Cars and Pedestrian Deaths."


Last year ended with a slew of pieces on the matter, and we're beginning 2024 with another set of study results on the topic. Justin Tyndall at the University of Hawai'i's Economic Research Organization authored the earlier study mentioned above, "Pedestrian Deaths and Large Vehicles." His new take on the data, titled "The effect of front-end vehicle height on pedestrian death risk," examined how high the front end of a vehicle needs to be to begin to show an outsized effect on pedestrian deaths. The abstract tells the tale of the results: "I merge U.S. crash data with a public data set on vehicle dimensions to test for the impact of vehicle height on the likelihood that a struck pedestrian dies. After controlling for crash characteristics, I estimate a 10 cm increase in the vehicle’s front-end height is associated with a 22% increase in fatality risk. I estimate that a cap on front-end vehicle heights of 1.25 m would reduce annual U.S. pedestrian deaths by 509."

Translating that starts with knowing that almost 7,400 pedestrians died after being struck by vehicles in 2021; in 2005, that number was 3,813 pedestrians. Tyndall says that a four-inch rise in the height of a vehicle's front fascia results in a 22% rise in the risk of pedestrian death. If regulators capped front fascia height at 49.2 inches, the numbers point to 509 lives being saved every year in the U.S., nearly 7% of 2021's death figure. 

Tyndall's paper follows last November's report by the Insurance Institute for Highway Safety about the same matter. And if the IIHS findings are accurate, it seems 40 inches of vehicle front fascia height begins to pressure the numbers. The IIHS wrote, "Vehicles with hoods more than 40 inches off the ground at the leading edge and a grille sloped at an angle of 65 degrees or less were 45 percent more likely to cause pedestrian fatalities than those with a similar slope and hood heights of 30 inches or less. Vehicles with hood heights of more than 40 inches and blunt front ends angled at greater than 65 degrees were 44 percent more likely to cause fatalities."     

Unlike the IIHS, Tyndall doesn't take the angle of the front fascia into account, the paper explaining, "[The] angle of a vehicle’s hood is generally similar across consumer cars and light trucks. Therefore the proposed method of estimating front-end height should capture the large majority of true variation across vehicles." All of which sounds like there's going to be more granular study of heights and slopes — and soon, vehicle weights — before we're ready to put a dividing line on just how tall a vehicle is too tall.

Lastly, one of Tyndall's interesting findings was that on the average vehicle, there's a 2.4-inch vertical rise from the leading edge of the hood to the windshield cowl. He writes that the number worked on the Toyota Corolla and the Ford F-150. Even more interesting: This Car & Driver piece from 2012 explaining how pedestrian regulations can start off as fractional adjustments that, in service to proportion and visual design, help result in larger vehicles sitting higher up on larger wheels.  

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