The NHTSA uses three tests. The first is a 35 mph frontal crash test. It determines what injuries a driver or passenger might experience in that type of accident. The second is a side-impact test (made up of two tests using different weights). The third test is not an actual test. It is a rating based on a mathematical formula based on the car's width and center of gravity. NHTSA uses a five star rating system. A single star is poor while five stars is the best rating. 