I am reporting a Sudden Unintended Deceleration event in my Subaru. The vehicle grinded to a halt without driver input. The car stopped in the left lane of a major highway. We put on our hazards and called the state police for help. They were unable to get to us in time. We were hit from the rear. The car's failure created a stationary hazard that led to a high-speed rear-end collision by a Jeep and truck which caused the car to do a 360-degree spin.