The new program will continue to assess passenger cars, pickup trucks, sport utility vehicles and vans on the five-star scale but will add an overall safety rating that combines scores from several crash tests.
The new system, which will start in the 2010 model year, also will include new front-end tests and a test in which the vehicle strikes a pole sideways to simulate the wrapping of a vehicle around a tree. Female crash test dummies will be used to represent women and large children.
"We're trading in the old program for a newer, more advanced model," said Transportation Secretary Mary Peters, who unveiled the changes at a Honda dealership in Vienna, Va.
The consumer program, started in 1979, has helped spur interest in safety equipment such as side-impact air bags and anti-rollover technology. But some auto safety advocates contend that most vehicles earn four or five stars on the tests, making it difficult for consumers to compare safety features.
In 1979, less than 30 percent of the tested vehicles received four or five stars, according to Peters. This year, more than 97 percent of the vehicles earned those high scores, she said.
Nicole Nason, who leads the National Highway Traffic Safety Administration, which developed the new testing program, said she expects fewer vehicles will earn five stars under the system, but the agency did not have a precise estimate.
Peters said the overall safety rating would combine results from front-end, side and rollover tests, taking out the "guess work" of comparing scores for different makes and models.
The new ratings will take into account a broad range of technologies to prevent crashes, letting car shoppers know whether electronic stability control, lane departure and forward collision warning systems are optional or standard features on a vehicle.
For the first time, the ratings will factor in the ability of vehicles to guard against leg injuries in head-on collisions.
Automakers and suppliers have pushed for the changes to reflect the benefits of electronic stability control and anti-rollover technology, which the government is considering requiring on all new vehicles beginning in 2012.
Wade Newton, a spokesman for the Alliance of Automobile Manufacturers, which represents General Motors Corp., Toyota Motor Corp., Ford Motor Co. and others, said, "safety is our top priority so we certainly understand the importance of getting consumers relevant information."
Joan Claybrook, president of Public Citizen, a watchdog group, said the changes offered some improvements, but the agency should have included test ratings for rear crashes, child restraints and a rollover test conducted while the vehicle is in motion. During the current government rollover test, the vehicle is stationary.
Claybrook, who led NHTSA in the late 1970s when the program was established, has also pushed for easier to understand school letter grades, such as A, B, C, D and F.
"It's still a very rough guide and we think it still needs to be substantially updated," she said.
On the Net: NHTSA's New Car Assessment Program: http://www.safercar.gov