I've posted it here before, but it bears repeating:
My brother is a fireman and paramedic. Last year, they had a fire truck severely damaged when a guy rear-ended it at full highway speed. The truck was parked in the road, all brakes locked, all lights running. There were several other emergency vehicles parked, all lights running, and a bunch of guys walking around a car fire with full gear on.

The guy came plowing in and slammed into the back of the fire truck hard enough to drive it forward 10 feet. They got what was left of the driver out of the pickup with a combination of jaws and a spatula, probably.

People can get completely oblivious when driving. This is why I not only light up and bright up, I use a mirror heavily. If you're approaching me from behind, I've been keeping an eye on you for at least a few seconds before you'll get close enough for me to have to make a "bail-out" decision. Usually if someone is pushing too close to me, I'll move a bit left, that wakes them up.