A car after an crash test, with a crash test dummy in the front seat
Photo: IIHS

Driving just a few miles per hour faster can lead to far worse injuries in a crash, even in a car with top safety ratings, a new study shows.

Government and independent crash tests that consumers rely on when purchasing a car can be a helpful gauge in comparing the crash performance of one vehicle vs. another. But those tests are conducted at speeds as low as 35 mph and therefore don’t reflect the added risk—and the danger—of real-world roadway speeds. For example, cars that earn a top score of “Good” in crash tests conducted at 40 mph by the Insurance Institute for Highway Safety (IIHS) would earn a “Poor” rating if those same tests were conducted at 50 mph, the research shows.

But that doesn’t mean that simply testing cars at higher speeds is the solution, says Joe Young, a spokesperson for IIHS, an insurance-funded research and advocacy group. (IIHS also co-authored the study.)

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“At first glance, increasing crash-test speeds sounds like a good way to improve design, but it actually could have unintended consequences,” Young says. “Stiffer structures required to perform well at higher speeds might actually make lower-speed crashes more dangerous, since crumple zones wouldn’t engage as well.”

Nor does IIHS argue that speeds on highways be lowered to 40 mph. That’s because other factors come into play when an actual crash takes place, Young says. “In the real world, you may have time to apply the brakes, or you might strike a vehicle from behind that is moving in the same direction, or you may strike something that weighs less than your vehicle,” he explains. “All of these things impact how much energy is involved in the crash.”

But IIHS does say that speed limits in some states have gotten out of hand. “We know that changes to the state speed limit have a direct effect on fatalities," Young says, "yet states continue to raise them.” 

At 40 mph, the vehicle's cabin remains intact after a crash. At 55.9 mph, it is deformed.
At 40 mph, the vehicle's cabin remains intact after a crash. At 55.9 mph, it is deformed.
Photo: IIHS

In addition, advanced safety systems such as forward collision warning (FCW), automatic emergency braking (AEB), lane departure warning (LDW), and blind spot monitoring (BSW) can help prevent crashes from happening in the first place, or at least reduce crash speeds, says Jennifer Stockburger, director of operations at CR’s Auto Test Center.

“This study shows that speed has a significant effect on the level of injury vehicle occupants may sustain,” she says. “So even if these systems can’t prevent the crash entirely, if they are successful in prompting an earlier reaction from the driver or vehicle that reduces the speed of the vehicle at the time of impact, they will provide benefits.”

One technology could be particularly helpful, says William Wallace, CR’s manager of safety policy. “Automatic emergency braking that works to prevent or mitigate crashes at highway speeds has enormous potential,” he says. “While many of today’s new car models come standard with city-speed AEB, and some come with pedestrian detection, highway-speed AEB is less common. Automakers should keep improving their AEB systems to save lives on the road.”

The study was authored by researchers from IIHS, the AAA Foundation for Traffic Safety, and Humanetics, a manufacturer of crash-test dummies. They crashed three similarly equipped 2010 Honda CR-V SUVs with similar mileage and maintenance histories at three speeds: 40 mph, 50 mph, and 55.9 mph. The CR-V was chosen because it represented an average vehicle on the road today in terms of age and size, and because the model got top “Good” crash-test ratings across categories when IIHS originally evaluated it. All three tests simulated a “moderate overlap” crash on the driver's side, which reflects what happens when a car has a partial head-on collision with a barrier or other vehicle.

Crash-test results showed that the vehicle’s safety structure couldn’t absorb the higher-impact speeds and transferred the force of the crash to the dummy inside the vehicle. In the real world, that means a driver who crashes at 50 mph has a “considerably lower” likelihood of surviving than one who crashes at 40 mph, the researchers say. 

Two cars after crash tests
The vehicle's structure did a better job protecting the driver in the lower-speed crash (left).
Photo: IIHS

It’s easy to see how: At 40 mph, the CR-V was damaged but the passenger compartment wasn't deformed—hence the “Good” score. At 50 mph, things changed. There was a higher likelihood of head and neck injuries, in addition to right leg injuries, which would have earned the CR-V a “Poor” score. And at 55.9 mph, the crash looked a lot worse. The dummy’s head was sticking through the broken window of the deformed driver's side door, its legs had been partially crushed, and its head had suffered a significant impact with the deployed airbags.

“Designing a car with good crash protection is a careful balance,” says Stockburger. Crumple zones and vehicle structures need to deform just enough that the vehicle absorbs some of the crash energy that would otherwise be transferred to the occupants. But they also need to be strong enough to limit the amount of intrusion and deformation into the vehicle’s passenger space, she says. “Speed can alter that balance in a negative way.”

The dangers of speeding have been even more pronounced during the COVID-19 pandemic, because fewer cars on the road make it possible to travel at higher speeds. According to the National Highway Traffic Safety Administration, speeds have increased 22 percent on average in some cities since the start of the pandemic. Fatalities are up—1.25 deaths per 100 million vehicle miles traveled for the first half of 2020, up from 1.06 for the first half of 2019—even though Americans are driving less.

According to Stockburger, less congested roads shouldn't be viewed as an invitation to go faster. “Something unforeseen can always happen," she says, "so be sure to always drive safely.”