Fewer than three of 10 drivers of cars with motorized "automatic" seat belts buckle their manual lap belts, which leaves them at a much higher risk of injury or death, a new study shows. The two-year study suggests that many drivers either forget to buckle their lap belts or are just too lazy to do so. Others do not know they have lap belts and need to use them.

If a door flies open in a crash, "a driver who has failed to buckle his lap belt is completely unprotected," said Donald Reinfurt, associate director of UNC's Highway Safety Research Center at the University of North Carolina at Chapel Hill, where the study was conducted. "We know the combination of automatic shoulder belt and manual lap belt is much more effective than either part by itself." Reinfurt was to present the study to the annual meeting of the Association for the Advancement of Automotive Medicine in Scottsdale, Ariz., today. It is the first look at the influence of automatic restraints on manual lap belt use in both rural and urban areas, Reinfurt said.

In the study, trained observers recorded belt use among drivers of 1986 and later-model cars who were stopped at traffic lights. Nearly 50 highway settings across the state of North Carolina were monitored on different days and at different times of day. Because neither car models nor motorists' attitudes vary much from state to state, Reinfurt said researchers believe the North Carolina data are typical of the entire nation.

Only 28.6 percent of the drivers in the study buckled their manual lap belts in addition to the automatic restraints.

About 80 percent of the drivers of newer cars with automatic seat belts were using them, while about 20 percent had disconnected the automatic restraints.

In an especially surprising finding, 76 percent of drivers -- three out of every four -- with older, manual seat belts were buckling up, nearly as many as were using the automatic restraints in newer cars. And 74 percent of drivers in cars equipped with air bags were using belts.

"People have a misconception that once they have air bags, they are fully protected, but that's true only for moderate or worse frontal crashes," Reinfurt said. "Air bags are not designed to inflate in other types of crashes such as side or rear impacts or rollovers."