A system of sensors and computers that alerts truck drivers when their rigs are in danger of rolling over could prevent as many as 4,000 accidents a year, according to researchers at Oak Ridge National Laboratory (ORNL). The rollover detector developed at ORNL consists of sensors in the trailer that measure the weight transfer at the rear axle and the lateral acceleration; that information is fed to an onboard computer that tracks in real time the truck's stability. In addition, the ORNL researchers have positioned at several curves roadside beacons that alert the approaching trucks. If the vehicle is in danger of rolling over, a warning sounds for the driver to slow down. The lab has equipped several trucks owned by U.S. Xpress Enterprises with the system, which costs about $7,000 for each tractor-trailer. The trucks are to begin testing it this summer as they rumble up and down Interstate 75.