Fuck, man, I'm so sorry.
The worst thing I've ever seen like that is when I was on a bus that was riding really closely with a cyclist. The cyclist fucked up and fell, and one of his legs went right under the bus. The full weight of that wheel went right over him, and the sound I heard him make is something I'll never forget. The bus immediately stopped, we all got out, and emergency services were called. The bus driver was horrified, and I can only imagine how tough that was for her, as well.
As far as the guy, man, I can't even describe what his leg looked like, except that it was pressurized skin, muscle, bone and blood. It was surreal.
I had to talk to people for a while after it happened, because it's so hard to forget after seeing something that grisly. You and the other person in your car should definitely try and take extra care of yourselves emotionally for a while. It's a traumatic experience.