The old "Stars on Cars" system, which assessed vehicles on front-end and side-impact crashes and rollovers, was started in 1979, and it has helped build interest in car safety equipment.
The changes to the old system come as too many cars were receiving top marks, which made it difficult to distinguish the best performers.
The new system takes into account the crash prevention technology some new models have, and it includes a new test that simulates a car crashing into a pole. This new test also includes female dummies to see crash effects on women.
Also for the first time, the vehicles tested will have the results of their star rating posted on a new window sticker on the car while it's in the showroom, but this may not happen for a few months.
The grading system ranges from one star to five stars, five being the best. Only two of the first 33 cars tested earned a five-star rating - the 2011 BMW 5 Series and the 2011 Hyundai Sonata.
"We've raised the bar on safety - more stars, safer cars. People really have to prove to us that these cars deserve a five-star rating," said U.S. Secretary of Transportation Ray LaHood.
The 2011 Nissan Versa got two stars while hybrid and conventional versions of the Toyota Camry received three stars.
Toyota responded to the new results with the following statement:
"This is caused by the new testing procedures, not because the vehicle is less safe."
The Alliance of Automobile Manufacturers, the auto industry trade group that represents various auto makers, said that ratings for new cars will probably go down, even in cases where there have been no significant changes to the vehicle.
Another 22 vehicles will be tested later this year.
The Associated Press contributed to this report.