NEW YORK (CNN/Money) -
The National Highway Traffic Safety Administration's new, more detailed, rollover rating still isn't telling you enough, some safety experts say.
The problems: how the agency uses test results to calculate the percentage chance each vehicle has of rolling over, and the way ratings are displayed on NHTSA's Web site.
NHTSA's new rating system does provide more information and makes it easier to distinguish among vehicles. But some consumer groups, including Consumers Union and Public Citizen, charge that for all the improvements in the new system, other longstanding problems remain and should be fixed.
Stars too broad
Complaint: Under NHTSA's old system, vehicles were given a star rating indicating how likely they are to tip over in a crash. The most unstable vehicles would get one star and the most stable, 5 stars.
For sport/utility vehicles -- the type of vehicle most prone to roll over -- the five star system became, essentially a two-star system. Only one SUV, the two-star rated 2-wheel drive Ford Explorer SportTrac, has anything other than three or four stars.
To make matters more confusing, the four-star rating for some SUVs would seem to imply that those SUVS are as stable as, say, a Jaguar X-type sedan. In fact, the SUVs only just make the four-star grade while sedans like the X-type approach 5-star stability.
NHTSA's solution: The new version of NHTSA's rollover ratings, released last week, addresses this problem.
|Detailed rollover rating for 2004 Buick Rainier
Although the star ratings remain, in a detailed information page for each vehicle you'll find a rollover rating graphic displaying that vehicle's relative rollover risk compared all vehicles of its class. The image shows a diamond positioned inside a white bar which represents the risk range for all vehicles of its type.
Complaint: Although NHTSA does a Dynamic Stability Test, which puts a vehicle through abrupt turns at speeds up to 50 miles an hour, that test has relatively little effect on a vehicle's star rating. If a vehicle passes the test, meaning that it keeps all three wheels on the ground at speeds up to 50 miles per hour, it might be moved up into the next highest star rating. Vehicles that do tip on the test see no change in their star rating.
Critics have complained that tipping should have a more serious result. Also, pass/fail results should be more clearly displayed on NHTSA's Web site and NHTSA should publicly reveal the exact speed at which the vehicle tipped.
NHTSA's response: Only five percent of vehicle rollovers occur because the driver simply turned the wheel too hard, according to NHTSA data. Most rollovers, by far, are "tripped" rollovers. That means the vehicle hits something, say a curbside or ditch, that undercuts it and sends it tumbling.
The Static Stability Factor is a much better predictor of the tendency to go wheels-over in that sort of situation, NHTSA says. Putting more emphasis on the dynamic test, then, would put too much emphasis on something that doesn't reflect real-world risks.
Joan Claybrook, president of the consumer advocacy group Public Citizen and a former NHTSA administrator during the Carter administration, says that NHTSA is using old data on rollover causes. Although she cannot point to specific data to support her contention, she claims that untripped rollovers account for a much higher percentage of rollovers than NHTSA says -- as much as half.
NHTSA spokesman Mark Krawczyk disputed the notion that the agency is using outdated numbers. NHTSA is relying on the most recent figures available, he said, which are about 10 years old.
One test's not enough
Complaint: There are some ways that vehicles could be made to perform better on NHTSA's current Dynamic Stability Test but which might not actually make the vehicle safer to drive.
For example, a vehicle with tires that don't grip the road as well would be less likely to tip over.
Instead, it would tend to skid and spin out. While that wouldn't be a desirable trait in real driving, it would earn a passing grade on this test.
The best way to prevent this kind of handling compromise is to have multiple tests rate various aspects of a vehicle's emergency handling capabilities.
NHTSA's response: NHTSA is currently working on a suite of handling tests that will measure a variety of different handling charecteristics. In the future, these tests will become part of a separate handling rating system, Krawczyk said.
Complaint: Electronic stability control is an option -- and a standard feature in some cars -- that significantly reduces the risk of loss of control and rollover situations.
Computers monitor various aspects of a vehicle's movement, including speed, steering, body lean and how fast each wheel is rotating, to determine if the car is in danger of spinning out or skidding. The instant an impending wipe-out is predicted, engine power is reduced and brakes are applied to individual wheels to bring things back into line.
While ESC could prevent many rollovers, its availability is not readily apparent in NHTSA's vehicle lists. Other safety features, like side airbags, are prominently noted in vehicle descriptions. To find out if a vehicle has ESC, though, Web site users must click down to each individual vehicle page. Even when a user does that, though, whether the vehicle tested had ESC or not is still not clear.
NHTSA's response: This is really a technical problem that NHTSA is working to fix, said Krawczyk. For now, the Web site interface doesn't allow that information to be more clearly displayed.
If a vehicle has ESC as standard equipment it is, of course, tested with that system. If it's optional, then the vehicle is tested with ESC only if the manufacturer certifies that more half the vehicles they sell will have that option installed. Once technical issues are resolved, said Krawczyk, the presence of ESC will be clearly displayed.