"Through new tests, better crash data, and higher standards, we are making the safety ratings tougher and more meaningful for consumers," Transportation Secretary Ray LaHood said in the statement.
Nissan Motor Co.'s Versa received the lowest overall rating of two stars, scoring four stars in rollovers, three in frontal crashes and two in side crashes.
The new crash tests include dummies representing women, who tend to be smaller than the male figures used exclusively in the past and may be harmed differently in an accident, according to NHTSA. The new dummies also collect data about injuries to the chest, head, neck and legs while the old ones measured only chest damage.
NHTSA has also begun compiling an overall rating for each model for the first time rather than reporting only the front, side and rollover collision results.
Automakers had questioned the redesigned safety ratings because they aren't directly comparable to the ratings they replaced, potentially creating confusion.
The agency said it is continuing to test cars and trucks and plans to add the results as they are complete to its website at safercar.gov.
In a statement, the National Automobile Dealers Association said: “We support the federal government's efforts to enhance safety information to allow for more informed purchasing decisions by vehicle shoppers."
The NADA said it would provide dealers with information about these points:
• New Car Assessment Program (NCAP) scores for model year 2011 may be lower than for previous models of the same vehicles, but that does not mean they are less safe, the NADA said.
• NCAP scores for 2011 and later vehicles should not be compared to those for previous model years, the NADA said.
• Overall ratings scores reflect a weighted average of the three crash test results. All new vehicles are subject to rigorous Federal Motor Vehicle Safety Standards, the NADA said.
• The NCAP label will not be updated until the 2012 model year. The best source of NCAP information is www.safercar.gov.
• Only 50 or so models are NCAP tested in a given model year, the NADA said. Test results are made public as they become available.