According to new Insurance Institute for Highway Safety (IIHS) research, the effect of crash speed on pedestrian injury risk is magnified for vehicles with taller front ends, beginning at lower speeds.

“The faster a vehicle is moving when it strikes a pedestrian, the more likely it is to inflict serious injuries,” states an IIHS press release about the findings. “Exactly how much more likely depends in part on the height of the vehicle, with taller vehicles compounding the risk from higher crash speeds.”

IIHS researchers analyzed pedestrian crashes to develop injury risk curves showing how speed affects crash outcomes. Compared with risk curves developed using crash data from Europe, where tall passenger vehicles are less common, risk curves for the U.S. show pedestrians begin to suffer more serious injuries at lower speeds, the result of “our fondness for tall SUVs and pickups in the U.S.,” according to IIHS President David Harkey.

“A small increase in crash speed can really ramp up the danger to a pedestrian,” Harkey said, in the release.

And height “has intensified that effect,” he added.

The findings suggest that the 25 mph speed limit commonly used in residential neighborhoods in the U.S. may be too high for bustling city centers or other areas with large numbers of pedestrians.

To estimate injury risk at different impact speeds, IIHS researchers examined 202 crashes involving pedestrians ages 16 or older. The records came from two databases — one of crashes that took place between 2015 and 2022 in Michigan and another of 2022 crashes in California, New Jersey, and Texas.

The researchers used photos of the vehicle models to determine the height of the hood’s front edge then looked at the effect of vehicle speed and height on the risk of injuries of different severities.

They focused on front-end height because that determines the point of impact on a pedestrian’s body, which is a key factor in injury severity, the release says. In contrast, IIHS says vehicle weight doesn’t play a major role in pedestrian crashes since any vehicle, even a small car, vastly outweighs a person

“Our findings suggest a similar fatality risk curve compared with past estimates from U.S. crash data but a slightly more pronounced relationship between impact speed and injury risk compared with research using European samples, with pedestrians suffering greater injury risk at lower impact speeds,” the report states. “The increased injury risk we observed likely stems from the composition of the U.S. fleet… Indeed, we found that greater vehicle height was consistently associated with greater injury risk overall, and in some cases amplified the risk from faster impact speeds.”

However, the researchers also found that regardless of vehicle height, higher speeds were associated with increased risk of injury at all severities, the release says.

“Pedestrians struck at 20 mph had a 46% chance of sustaining at least a moderate injury, such as a broken bone or concussion, and an 18% chance of a serious injury, such as a broken bone that protrudes from the skin,” the release says. “At 35 mph, the risk of moderate injury climbed to 86% and the risk of a serious injury rose to 67%.

“As far as fatalities were concerned, pedestrians struck at 20 mph had only a 1% chance of dying from their injuries but at 35 mph, the risk reached 19%; at 50 mph, it exceeded 80%.”

In general, higher vehicle front ends used in the tests increased the likelihood of moderate and serious pedestrian injuries.

At 27 mph, the average speed of all 202 crashes, a median-height car had a 60% chance of causing moderate injuries to a pedestrian and a 30% chance of causing serious injuries. In comparison, a median-height pickup — with a front end 13 inches higher than a median car — had an 83% chance of causing moderate injuries and a 62% chance of causing serious injuries.

“This tracks with earlier IIHS research that found that vehicles with taller front ends are more likely to kill people when they hit them,” the release says. “In the new study, fatalities followed the same pattern as moderate and serious injuries but the effect wasn’t statistically significant.”

The study’s authors compared the risk curves they generated for the effect of speed with risk curves published in 2022 based on crashes in Germany. They found that pedestrians in the U.S. are more likely to be injured at all speeds. Hypothesizing that differences in vehicle size were to blame, they used the U.S. data to generate new injury curves for the median-height pickup and median-height car. The car curves are close to the German curves while the pickup curves are shifted left, indicating increased risk at lower speeds, IIHS said.

“Although SUVs are a growing share of the market in Europe, the passenger vehicle fleet there has long been dominated by cars,” said Sam Monfort IIHS senior statistician and the study’s lead author, in the release. “In contrast, the majority of passenger vehicles on U.S. roads today are SUVs or pickups,”  “These choices have very real consequences for pedestrian safety.”

The serious injuries risk curve for the median pickup is also steeper.

“In other words, speed increases have a more pronounced effect when taller vehicles are involved,” IIHS said. “For example, as crash speed increases from 15 mph to 35 mph, the risk of a serious injury goes from 9% to 52% when a median-height car is involved. With a median pickup, the risk shoots up from 11% to 91%.

“The findings point to the need for policymakers and traffic engineers to account for the makeup of the U.S. fleet when thinking about speed limits and traffic calming.”

A commonly used benchmark for a “safe” crash speed is one at which the risk of serious injury is 10% or less. In this study, that threshold occurred at about 15 mph. That means even a 25 mph limit may be too high for areas with a lot of pedestrian traffic, IIHS said.

That said, IIHS concluded that small reductions above that level could have enormous benefits for pedestrians as well. Cutting crash speeds from 30 mph to 25 mph, for example, would cut serious injury risk by more than a third, from 50% to 32%, according to IIHS.

“Vehicle manufacturers also have a role to play in preventing pedestrian crashes and mitigating those that still occur,” IIHS said. “They could, for example, modify their front-end designs and equip vehicles with more robust automatic emergency braking systems.”

Harkey added, “This study is a vivid illustration of how multiple factors — in this case speed and vehicle height — converge to create negative outcomes on the road. Similarly, it will take a combination of actions from different corners of the transportation world to improve pedestrian safety.”

In October, the Road to Zero Coalition released research that included recommendations for federal, state, and local governments as well as vehicle drivers to improve hazards it said are caused by bigger, heavier pickup trucks.

Pickup trucks, SUVs, and vans account for nearly 75% of vehicles produced today, according to the coalition.

Features of larger and heavier vehicles (including electric vehicles) that make them “so deadly,” according to the coalition, include:

• • Height and weight relative to pedestrians
  • Crash incompatibility with smaller cars
  • Unique front-end geometry and stiffness
  • Large blind zones
  • Compounding impacts of speed and acceleration

The number of pedestrian deaths involving SUVs, pickup trucks, and vans rose about 77% between 2012 and 2022, while during the same period, the number of sales and leases of such vehicles increased by 50%, according to the coalition’s report.

Images

Featured image and graphs provided by IIHS. Interactive use of the graphs is available here.