Chances are that the sensors hat are supposed to prevent that sort of thing were: 1. Never put on, because the bus was designed to be cheap, not safe 2. Broken, and was never repaired because it's not an issue that will kill everyone on the bus, just the poor sod left being dragged. 3. Deliberately taken off to be sold, used somewhere else, or somehow used to cut costs. If it was any of those situations, yes, OP actually COULD file a lawsuit and would have a decent case and shot at winning, especially if the city is supposed to maintain them on a regular basis and either didn't do so, or did and passed it despite it missing an important part. It's almost be worth filing the claim even on a losing case so that the company has to fix it before a small child or elder get caught in it- they wouldn't get away with just a bruised arm.