Tire Blowout problems of the 1999 Saturn SL1

I was driving on a highway at about 50 mph as the rear passenger tire blew out, I lost control of the car, swerved over a lane then off the highway, hitting the curb and ending up in a grassy area. The police arrived and courtesy patrol arrived to assist in changing the tire. Their objective was to immediately get me on my way, so the courtesy worker threw my tire into the trunk and I left. When I got to the tire store we evaluated the tire and 40% of the tire had separation. The car has maintenance done every 3000 miles, so tires were rotated and properly inflated. ( dot number: w2epbca428 tire size: p17570r14 ).