The National Highway Traffic Safety Administration is a U.S. government agency in charge of conducting vehicle safety tests. The NHTSA operates the New Car Assessment Program, which gives a rating out of five stars based upon rollover and crash tests.
Not all vehicles in the market are tested by the NHTSA. The Insurance Institute for Highway Safety also tests vehicles, though Edmunds.com notes that it also does not test every vehicle. Both institutions, do however, test all major vehicles. Edmunds.com notes that cars tested before 2011 by the NHTSA cannot be compared to newer cars because the testing criteria became more stringent in 2011.