Although we often don't think about it, vehicle safety is a major part of engineering and designing a car, truck, or SUV. Yet, we simply look at a star figure and make our judgments.
What exactly does a five-star crash test rating mean? It's the descriptor so many brands will use to underscore vehicle safety in advertising, and Jason Fenske of Engineering Explained is here to, well, explain it.
First, we need to point out this video involves NHTSA crash testing. The insurance-funded IIHS does things differently, but the NHTSA is the official U.S. government safety score. The agency looks at three areas: a frontal crash, side-impact crash, and a rollover crash. Two crash test dummies are placed inside the car for the frontal test, and after the crash test is complete, official take measurements and gather information.
The information they gather helps paint a picture of the likelihood a driver or passenger would sustain injuries in the particular crash test. On the five-star scale for the frontal rating, a five-star rating means there's a less than 10 percent chance the driver or passenger would sustain major injuries. Moving down to a one-star rating means there's at least a 40 percent chance of a major injury.
Tesla Model 3 NHTSA test
It's important to note that it's difficult to compare vehicle safety based on frontal crash-test ratings. Only cars with weights within about 250 pounds of each other should be compared since a heavier and lighter vehicle involved in a crash will behave very differently.
The side-impact test follows a nearly similar formula, which involves two tests. The first is a crash test mimicking a car slamming into the driver's side of the vehicle, while the second looks at a different scenario. Here, the test calculates how a car crashes if the driver loses control and slides off the road into a telephone pole. Once again, the star rating amounts to the probability of a serious injury occurring as in the front crash test. Unlike the frontal crash test, we can compare safety regardless of weight because both tests are exactly the same.
2013 Smart Fortwo Electric Drive NHTSA crash test (Image via crashnet1.com)
Finally, the rollover rating. The scenario is where the vehicle slides off the side of the road, and in the process, proceeds to roll over. There's a big difference in this test, though. Unlike the front and side crash tests, the star rating is based on the probability of the vehicle rolling over—not sustaining major injuries. Here, the agency looks at a car's static stability factor (track width and a center of gravity's height). Thus, a wider car with a bigger track width has a lower probability of rolling over compared to a more narrow vehicle. On the other hand, a car with a lower center of gravity is also less likely to roll over.
The star rating still follows the same probability factors. One star means there's a 40 percent or greater risk, while a five-star rating leaves a less than 10 percent risk.
After all of the tests, the crash-test ratings will be calculated and tallied into an overall rating to give cars an overall rating of, say, five stars. Dive into more details on how crash tests and ratings work in the video above.