Taller vehicles make lower-speed crashes more dangerous for pedestrians

Article content

• A new IIHS study finds that vehicle height magnifies the effect of speed on pedestrian injury risk
• Being hit by a pickup truck can more than double the risk of serious injury versus being struck by a car
• And taller vehicles are increasing the injury risk even in lower-speed pedestrian crashes

Vehicle speed is a factor in how severe injuries are when a pedestrian is struck, but the vehicle’s height also plays a part. According to a new study by the U.S. Insurance Institute for Highway Safety (IIHS), taller vehicles compound the injury risk of high vehicle speeds. “A small increase in crash speed can really ramp up the danger to a pedestrian,” said David Harkey, president of IIHS. “Our fondness for tall SUVs and pickups in the U.S. has intensified that effect.”

The researchers analyzed pedestrian crashes to see how speed affects the outcome of crashes, and found that vehicles with taller front ends magnify the effect of crash speed. They then compared data from Germany, where taller vehicles aren’t as common. Comparing the resulting risk curves, they found that pedestrians in the U.S. “begin to suffer more serious injuries at lower speeds.”

The researchers looked at front-end height because it determines the point of impact on the pedestrian, a key factor in injury severity. Vehicle weight doesn’t play a major role, since every vehicle vastly outweighs a pedestrian.

In all cases, higher speeds increase the risk of injury and at all levels of severity. Pedestrians who are hit at 20 mph (32 km/h) have a 46% chance of at least moderate injury, such as a broken bone; and an 18% chance of serious injury, such as that bone protruding from the skin. At 35 mph (56 km/h), moderate injury risk rises to 86%, and serious injury to 67%. For pedestrian fatalities, only 1% of those struck at 20 mph (32 km/h) had a chance of dying from their injuries, but the risk rises to 19% at 35 mph (56 km/h). When struck at 50 mph (80 km/h), a pedestrian’s risk of being killed is more than 80%.

The new study looked at 202 crashes, which had an average speed of 27 mph (43 km/h). At that speed, a “median-height” car had a 60% chance of causing moderate injuries, and a 30% risk of serious injuries. Researchers then looked at a median-height pickup, that is, one with its front end 13 inches (330 mm) taller than the median-height car. At the same speed, the risk of moderate injuries rose to 83%, while serious injury risk rose to 62%.

When they compared the U.S. findings to the crash data from Germany, the researchers found the risk from median-height cars was similar; but that of taller pickup trucks indicated increased risk at lower speeds. As crash speed increases from 15 mph to 35 mph (24 km/h to 56 km/h), the risk of serious injury from a median-height car increases from 9% to 52%; but with a median-height pickup, the risk increases from 11% to 91% with the increase in speed.

The IIHS released a report last year that concluded that vehicles with taller front ends are more likely to kill pedestrians when they hit them. In the new study, fatalities “followed the same pattern as moderate and serious injuries, but the effect wasn’t statistically significant,” the IIHS said.

The non-profit organization also said 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 common benchmark for a “safe” crash speed is one with less than a 10% risk of serious injury. In the new study, that happened at about 15 mph (24 km/h). The IIHS said “that means even a 25-mph (40-km/h) limit may be too high for areas with a lot of pedestrian traffic.”

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