Ford Motor Co. will install new side air bag "curtains" on its '01 Explorer and Mountaineer - at least surreptitiously addressing the long-held understanding that sport/utility vehicles (SUVs) are more prone to rollover-type accidents.

The new air bags, do, however, provide standard side-impact protection as well.

Ford's side-curtain system, under development for 30 months, will be launched on the Explorer and Mountaineer and then later added to the redesigned '02 Expedition and Navigator, due out in 2001.

Ford says the curtain air bag will be optional equipment for some SUVs, but eventually plans to offer the curtain air bags on SUVs worldwide. The expensive safety feature will not be offered on the all-new Escape at launch, but may be offered later as optional equipment.

"My expectation is that we will offer this system wherever our SUVs are sold," says Helen Petrauskas, Ford's safety and environmental engineering chief. She adds that utes are often bought for their perceived "bigger is better" attributes. Yet because of their high ride heights - and thus their propensity to roll - SUVs can be a mixed blessing.

"SUVs are as safe or safer in protecting their occupants from serious injuries or fatalities as like-sized passenger cars, but they do tend to be involved in different types of accidents," she says.

The Ford Windstar will get the curtain air bags next, but there are no plans for cars yet. The current side air bags in the Windstar that deploy from the seat to protect the head and chest in a side impact will be phased out in favor of the curtain air bags. The curtains are being supplied by Autoliv Inc. and TRW Inc.; the control modules by Delphi Automotive Systems, Robert Bosch Corp., Siemens Automotive, Takata Inc. and Visteon Automotive Systems.

The module - incorporating an advanced new roll sensor - is located in the drive tunnel between the driver and passenger and is designed to measure the degree of tilt and rate of roll. The system can tell the difference between an SUV navigating a steep slope or one that is involved in a roll that is unrecoverable.

The curtain air bags will use new "cold-air" inflators that keep the bag fully inflated for at least six seconds.

Ms. Petrauskas says the curtain air bags will offer better protection for people involved in rollover accidents and side impacts. Although less than 4% of light-truck crashes are rollovers, about half of the rollovers that do occur result in death. The curtain air bags also could help keep unbelted occupants in a vehicle during a crash. A person is three to seven times more likely to be severely injured when thrown from a vehicle during a crash.