Yesterday on my commute I also threw the chain (I guess): stopped for a right turn (US left turn equivalent) on in the middle of a major artery road, but when I started to pedal CLICK! chain snapped somehow and I almost went on my face. Safe, but the chain was destroyed. Looking at it at the edge of the road it seemed to have got stuck b/t derailleur and guard, maybe. Anyway I locked it up and took the train to work.