Arnold Schwarzenegger was just involved in a bad car accident ... so bad his monster SUV rolled over on top of another car, and that driver was badly injured.
Arnold was driving a Yukon SUV when it collided with a red Prius at around 5:00 PM PT. His SUV started to roll and ended up on top of the Prius, then continued rolling to the left into a Porsche Cayenne.
One eyewitness says it was crazy ... it looked like a stunt in a movie.