WASHINGTON (Sept. 5)—The National Highway Traffic Safety Administration has upgraded its investigation of Firestone ATX, ATX II and Wilderness AT tires to an engineering analysis from a preliminary evaluation. NHTSA began the investigation May 2, amid growing reports of tread separations and accidents involving the tires. During the preliminary analysis, the agency asked Bridgestone/Firestone Inc. for paperwork on the tires. Upgrading the investigation means agency engineers will study the evidence. If NHTSA finds a defect in the tires, under law it will have the right to order Bridgestone/Firestone to recall all 47 million ATX, ATX II and Wilderness tires made since 1991, not just the 6.5 million the tire maker voluntarily recalled Aug. 9.