Pursuant to a congressional request, GAO reviewed the National Highway Traffic Safety Administration's (NHTSA) crash test programs, focusing on whether they provide valid and reliable indicators of occupant safety in real world crashes. GAO found that: (1) the probability of sustaining a serious injury has declined since the inception of NHTSA test programs; (2) cars marketed in the United States have become more crashworthy; (3) the consistency of New Car Assessment Program (NCAP) test results is questionable and its unreliable data may lead to misinformed purchasing decisions; (4) NCAP ability to predict a vehicle occupant's protection in real world crashes is limited, since NCAP results can only be applied to frontal collisions; and (5) there is a statistically significant relationship between fatality rates and NCAP-predicted injuries, however, these high fatality rates are associated with the poorest NCAP performers.