Who is negligent if a vehicle stops in the middle of the road and is rear ended?

Generally, it is the person who hits the person in front of them that is At Fault. Unless, the person in front just stops for no reason like turning or something in the road. There are incidents in insurance fraud where a driver will stop on purpose to cause an accident. It is very hard for the person who hits them to prove that is why they stopped, but it can happen. I almost had it happen to me on the LA freeway several years ago. Had fellow pull in front of my car and just stop. I had enough space between us and was aware of the road so it didn't work, but it could have.