Crash-test ratings from the NHTSA are a key part of car buying and car selling. Anyone selling cars wants good ratings they can brag about, while anyone buying cars wants to steer clear of lower-rated models. When it comes to buying and selling cars, NHTSA ratings can mean big business.
That's why the NHTSA tries to take the business out of its ratings as much as possible. New car crash testing falls under the NHTSA's New Car Assessment Program (NCAP). As part of the program, new cars are crash tested under similar conditions, so consumers can easily compare the data. As part of the program, the NHTSA performs front and side impact crash tests, as well as rollover tests, to give its ratings.
Front crash tests are performed by crashing a car into a barrier. The goal is to simulate a collision between two similarly-sized cars, each traveling at 35 miles per hour (56.3 kilometers per hour). It's important for consumers to remember that when it comes to ratings, they only show how the car might perform in a crash with a car that's the same size, not crashes in general. Remember, if you're buying a car that's smaller than anything on the road, the crash test ratings don't necessarily apply if you crash into a much larger vehicle. On the plus side, since consumers tend to shop for cars by size, it's easy to see how the cars you're considering compare, since each is essentially crashed into itself.
Side-impact crash tests use a barrier that smashes into the side of the car. The test simulates a crash between two similarly sized cars, one traveling at 34 miles per hour (54.7 kilometers per hour) and the other traveling at 17 miles per hour (27.4 kilometers per hour). Again, the results only apply to collisions between cars of similar sizes, but they do provide a standard comparison for car shoppers.
The NHTSA also gives roll over ratings to each car. Those ratings are created through what the NHTSA calls "dynamic vehicle testing," where NHTSA tests how stable the car is by quickly changing directions and also by measuring the height of the car's center of gravity and how wide its track is. As a general rule, cars with a wide-track and a low center of gravity are less likely to roll over than tall, thin vehicles.