Who is at fault if car one has been pushed from a service ramp onto the main highway by car two?

Sounds confusing, but there seems to be a fair amount of fault all around. Was car #2 pushing a disabled vehicle onto the highway, or did he rear-end #1 on the service ramp? If disabled, it shouldn't have been on the highway except behind a tow truck (I know, lots of us have done it, but it's still against the law.), so whoever was behind the wheel and the pushing driver were both at fault. And if it was an accident on the ramp, #2 was definitely at fault.