For what it's worth these are my methods for dealing with icy bridges:
It goes without saying that you should slow down as much as possible before you reach the bridge. If I am not towing, i.e. truck camper, I try to maintain a steady speed, neither slowing down nor speeding up, while on the bridge. If I am towing, I slow down slightly as I cross the bridge. When towing you are putting a little more power to the driving wheels to drag the trailer so the tires are more likely to break loose if you are trying to maintain a constant speed. I also recommend you keep aggressive M&S tires on the rear of your tow vehicle year round.