Stability Control Systems and Rollovers

It is also true that high-stance light trucks are more likely to roll over than ground-hugging cars-more than three times as likely. Small SUVs are particularly prone to roll. Light trucks will often roll when they are "tripped"-a driver will hit a curbside or other obstruction that initiates the roll. In fact, driver behavior is at the root of many, if not most, light truck fatalities.

About 60 percent of the deaths in SUVs occur during rollovers when passengers are ejected. Had they been wearing seatbelts, they wouldn't have been ejected. Moreover, many light-truck drivers persist in driving their vehicles as they would a car, speeding around corners and risking loss of control.

To address the rollover issue, more automakers are installing stability- or skid-control systems on their light trucks. The systems use sets of sensors that automatically activate anti-lock brakes to help keep a vehicle from entering into a sequence of events that could lead to a rollover. If the sensors detect the vehicle moving in an unintended direction, the system briefly applies one brake to prevent the vehicle from spinning. A spin would cause the driver to lose control, perhaps allowing the vehicle to be tripped, which would then cause it to roll. BMW, Cadillac, Ford and Mercedes-Benz are among manufactures equipping SUVs with electronic stability-control systems.

In addition, NHTSA has recently begun issuing "Rollover Resistance Ratings." The agency awards the ratings-from one to five stars-using a mathematical formula that calculates how top-heavy a vehicle is based on its width and the height of its center of gravity. The ratings are listed on the agency's Internet site, www.nhtsa.got.gov.