Crash test ratings are just one way that auto safety experts inform you about the safety of the vehicle you own or want to own. However, they offer a fairly decent picture and carry a lot of weight.
According to U.S. News and World Report, there are two organizations that provide crash test information: the National Highway Traffic Safety Administration and the IIHS.
What the tests tell you
The main idea behind the tests is to encourage automakers to make better vehicles, and it works. When an organization tests a vehicle, it does so for specific types of accidents. The auto manufacturer sees the results and then works on future models to make them perform better in the test. So, for you, this means the future model will be even better.
As automakers manufacturer vehicles that pass the crash tests, the testing organization create different tests. Each test will add more crash scenarios, covering many different types of accidents. This encourages the automakers to keep improving, so every model gets better with each improvement.
How the tests work
Each testing organization conducts four tests. The IIHS does two front crashes where the crash point is off-center, a test for roof strength and a side crash. The NHTSA does two side crashes with one from a stationary object and one from another vehicle, a rollover and a front crash.
You should note, though, that these organizations do not test every single vehicle. In addition, the tests only rate each vehicle on its own and in a controlled environment without weather conditions.