The National Highway Traffic Safety Administration (NHTSA) has announced that 15-passenger vans have a high rollover risk when fully loaded and should be operated only by experienced drivers. NHTSA issued the rare consumer advisory April 9 after finding the vans are three times more likely to roll over when carrying 10 or more passengers than when carrying a lighter load. The study was prompted by a recent series of rollovers involving college sports teams. Four members of the Prairie View A&M University track team were killed and seven others were seriously injured when their van rolled over on the way to a meet last year. Other serious rollover accidents last year involved the Wisconsin-Oshkosh swim team, the DePaul women's track team and the Kenyon College swim team. NHTSA found that when fully loaded, a large van's center of gravity shifts up and to the back, increasing the risk of rollovers, especially in panic maneuvers by drivers. Officials from General Motors Corp., Ford Motor Co. and DaimlerChrysler AG agreed that van drivers need to be especially cautious. Ford, which makes the top-selling Econoline, warns drivers in its owner's manual to avoid sharp turns, excessive speed and abrupt maneuvers, but the other two manufacturers do not. NHTSA officials said there are about 1.4 million 15-passenger vans registered in the United States. In its study, NHTSA examined van crash data from seven states from 1994 through 1997. It found that 12.7 percent of the single-vehicle crashes with fewer than 10 occupants were rollovers, compared with 35.4 percent of accidents with 10 or more people. When 16 or more people were in the van, the number jumped to 70 percent. Experts say rollover risk can be reduced if owners buy high-quality rear tires, keep the gas tank as full as possible and drive conservatively. Passengers should fill front seats first and nothing should ever be loaded on the roof.