For the first time, federal regulators released figures yesterday that show how prone individual models of new cars and light-duty trucks are to roll over in an accident, exposing the occupants to high risk of death or serious injury.
Instead of merely assigning a star rating to each model it tests, as it has done in the past, the National Highway Traffic Safety Administration released figures that allow consumers to compare rollover risk model by model. The star system, which is continuing, has been criticized for not providing enough information to distinguish among vehicles, because nearly all received three or four stars.
Of the 68 models the agency tested for the 2004 model year, the Ford Explorer Sport Trac, a cross between a pickup and a sport utility vehicle, was found to have the highest rollover risk. The agency's tests indicated a 35 percent chance of rolling over during a single-vehicle accident.
That is more than four times the risk of the best performer in this year's tests, a four-door Mazda RX-8 sedan, which was about 8 percent, the agency said. Mazda is an affiliate of the Ford Motor Company, which makes the
Explorer.
As expected, cars performed much better than S.U.V.'s or pickup trucks in the tests, because cars are not as tall and generally ride closer to the ground, making them more stable. But the new ratings also show wide differences among vehicles of the same type.
For instance, versions of the Chevrolet Silverado pickup, made by General Motors, were judged to have a 16 percent to 18.5 percent risk of rollover, while one version of the Tacoma pickup from Toyota was rated as high as 28.3 percent.
"This is a problem that continues to produce about a third of our occupant fatalities every year, even though they are less than 3 percent of our crashes," Dr. Jeffrey W. Runge, the administrator of the traffic safety agency, said of rollovers.
The new rankings information, he said, "does arm the consumer with a little more sophisticated information."
Gloria Bergquist, a spokeswoman for the Alliance of Automobile Manufacturers, an industry lobbying group, said it was difficult to rate an automobile "like you rate a movie."
"This is just one rating," she said. "We urge people to look at all information and make a judgment, including the front impact and the side impact ratings."
The new rollover rankings, along with front and side impact test ratings, are available at the safety agency's Web site,
www.safercar.gov.
The agency also reported that the Ford Escape S.U.V. tipped up on two wheels during a rollover test; it was found to have a rollover risk of 21 percent to 24 percent - the same risk assigned to its corporate twin, the Mazda Tribute, which the agency did not test but which is essentially the same vehicle.
Kristin Kinley, a spokeswoman for Ford, said, "While we believe the N.H.T.S.A. rating system has some value, we don't think it's the most effective indicator of how vehicles perform in the real world."
Consumer groups have said the agency needs to do more to make the ratings available to the public.
"We compliment the agency on improving its presentation," said Joan Claybrook, president of the consumer advocacy group Public Citizen. But "significant flaws remain," she said, noting that the information was still not very easy to find. She said the agency should also establish a minimum performance threshold for rollover risk.
While the Explorer Sport Trac was the worst performer overall, the 2004 Subaru Outback wagon was the worst performer among passenger cars, a category that includes sedans and station wagons, with a 15.5 percent rollover risk. Other vehicles that combine aspects of wagons and S.U.V.'s, like the Nissan Murano, performed similarly, though some were counted as light-duty trucks; one, the Chrysler Pacifica from DaimlerChrysler, was ranked as the best performer in the S.U.V. group, with a 13 percent to 14 percent risk.
Rollover accidents kill more than 10,000 Americans a year, and have become a major traffic safety issue because of the popularity of sport utility vehicles and large pickup trucks. Drunken driving and failure to wear seatbelts also contribute to the high death toll in rollovers, as they do in other accidents.
While the high ground clearance of light-duty trucks can make drivers feel more in control, it also raises the vehicles' center of gravity, making the trucks easier to tip. Even so, manufacturers have powerful financial incentives to sell S.U.V.'s and pickups, not least that those vehicles are subject to considerably less stringent fuel economy regulations than cars.
Subaru, for instance, redesigned the Outback for the 2005 model year, raising its ground clearance and making other changes, allowing it to qualify for the lower truck standard. A Subaru executive said yesterday that the company expects the 2005 Outback to do better in rollover tests than the 2004 model, despite being taller, because other dimensions have also been changed.
The four minivans tested by the agency were found to have rollover risks of 12 percent to 16 percent, at the high end of the car ratings but lower than most light-duty trucks. Several S.U.V.'s. were rated above 25 percent, including the Chevrolet Tahoe, the GMC Yukon, and some versions of the Ford Explorer and Mercury Mountaineer.
The government rollover tests began this year at the direction of Congress, which ordered the agency to develop a track test in the wake of a series of fatal rollover crashes in the late 1990's involving Ford Explorers equipped with Firestone tires.
In the new tests, vehicles are driven through as many as 10 fishhook maneuvers, a jarring series of turns intended to replicate what happens when drivers momentarily lose control and veer to overcompensate. Last week, G.M. said it would recall its Saturn Vue S.U.V. because the vehicle's suspension broke during the test.
Previously, the government assessed rollover risk based on the vehicle's dimensions and a mathematical formula, without performing tests. Those calculations remain at the heart of the agency's evaluations, with the new track test information added.
Regulators are also looking into adding another test to assess handling, with its own star rating. One reason is that manufacturers can make a vehicle less prone to roll over in the tests by changing its tire specifications in ways that also make it less maneuverable.
"The idea of the handling test is, you can achieve good rollover resistance by degrading the handling of the vehicle, and that's not something we want," said Garrick Forkenbrock, a research engineer at the traffic safety agency. "It's no good if it's robbing Peter to pay Paul."
