- The Washington Times - Friday, December 7, 2001

Each year, vehicle rollovers account for about 10,000 fatalities in the United States. That's a sobering figure.

Most of the public became acutely aware of the possibility of vehicle rollovers during the Firestone tire controversy. In January 2001, the National Highway Traffic Safety Administration came forward with rollover ratings that try to estimate how likely a vehicle is to roll over if it goes off the road into a ditch, soft earth or deep snow.

NHTSA ratings are based not on crash tests but on measurements of a vehicle's height and width. Congress ordered the agency to have a new system in place in 2002, based on a handling test, one in which the vehicle is driven, not just subjected to a slide rule evaluation.

The current rating calculations divide half of a vehicle's track width by the height of the center of gravity. The track width is the distance from the center of one front or rear tire to the center of the tire on the opposite side. The result is called the "static stability factor." According to NHTSA, the larger the static stability factor, the more stable the vehicle. The smaller the factor, the more top-heavy the vehicle is and the more likely to roll over.

The agency then translates the static stability factor, or SSF, into the already-established star rating system it uses in interpreting the results of its frontal- and side-impact crash tests. Under the rating system one star is the worst and five is the best. The lowest-rated (one-star) vehicles are at least four times more likely to roll over than the highest-rated (five-star) vehicles.

Looking at the ratings for the 2001 and some 2002 vehicles currently on NHTSA's Web site, some generalizations can be made: Passenger cars get the most stars, meaning they are the least likely to roll over because they are lower and wider. And sport utility vehicles get fewer stars because they are taller and narrower. Here is a snapshot.

All passenger cars received four-and-five star ratings. Minivans, which included the Chrysler PT Cruiser, got three and four stars. Pickup trucks got two, three and four stars. The sport utility that performed the best was the Pontiac Aztek, with four stars. The ratings are heavily based on car components, which help reduce its center of gravity. Of the roughly three dozen sport utilities that the NHTSA evaluated during the past year, most have three stars for rollover risk.

A few, however, such as the 2002 Jeep Liberty and 2001 Nissan Xterra, got two stars, and the 2001 Chevrolet Blazer got one star. But the 2002 TrailBlazer did much better with a three-star rating. The redesigned 2002 Ford Explorer with four-wheel drive did better, too. It got three stars, while the 2001 model got two.

Both automakers and safety advocates have objected to the current rating system because it does not take into account more important factors such as a vehicle's handling and suspension. NHTSA, however, argues that it compared its calculated ratings to 222,000 real-world crashes and that the results related very closely.

Also, the system doesn't take into account the role that electronic stability control systems can play in helping drivers maintain control of a vehicle that begins to skid, an event that could turn into a rollover for a tall vehicle. In its ratings, NHTSA mentions which vehicles have electronic stability control but does not factor it into the equation.

To get rollover ratings, call NHTSA's toll-free Auto Safety Hotline, which is 888/DASH-2-DOT (888/327-4236) or visit the agency's Web site: nhtsa.gov.


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