How may collisions usually in a motor vehicle crash?

One, if you only count the exact second fracture when the crash happens.

Multiple, if you count all the collisions directly resulting from a crash. For example from ripped off parts of the vehicle fall on the ground, the person driving hitting the wheel, or the objects inside the car colliding together and falling to ground.

One could say "as many collisions in a crash as there are individual moving objects"