Part way witnessed an accident in my rear view mirror on this afternoon's commute. 43F and sunny with winds from the WNW @ 13mph. It happened a little over 100 feet behind me and the vehicle was going in the opposite direction as me. Not exactly sure what happened, but I know there was also a bus behind me at the time, who I believe was turning. Don't know if the bus had anything to do with it but I know the bus was never actually hit. I heard the tires skidding and looked in the mirror to see the car that passed me seconds ago slam into the car in front of him. I saw another vehicle stop, put on hazards, and the people jumped out to see if everyone was all right. It was kinda nerve racking to witness (and hear) something like that happen just right behind me. Later down the road, I saw the responding police car go flying by with flashers and all. Besides that, it was a good commute home.