I recently stopped at a red light and saw in my mirror an emergency vehicle with flashing lights approaching in my lane. I knew that I should move out of his path but that would entail crossing the stop line to move into the right hand lane. I was lucky in this instance that the emergency vehicle swapped to the lane on my left and turned off, so I didn't need to take any action, but what is the correct course of action in such a situation and was the law ever clarified on this point?