Hit the rear end of the fire-truck ? ... happens more often than you'd imagine
In Ireland and the UK (and presumably other European countries ?) - the guidance given to emergency services / blue-light response teams on major roads (with vehicles travelling at speed) is to park at an angle to traffic - not "in lane"
This was after a considerable number of expensive UK motorway police cars (big Volvos / BMW estates etc) being written off by drivers ploughing into the rear of them while they were stopped, lights flashing etc - but in line with traffic.
It's to do with the "looming" effect - that we perceive something as moving when it's not (or not moving when it is) - if it doesn't seem to change shape as we approach it .. the visual cues that the vehicle was stopped may only have appeared at the last moment.
The back end of a fire-truck with lights flashing is something we see moving more often than not - and they're big enough that while we see them, we think they're moving if they're in line with the lane and our approach - right until about 2 seconds out at 65mph when we exclaim "oh bugger!" - On the flipside - if we see the broadside of a truck / diagonally parked in the lane - we slow the hell down - as it's even bigger, and obviously going nowhere !