In either case, (with you moving or not), you cannot affect how much of a "hit" one car takes relative to the other car. The only things that affect how hard the "hit" will be are the differential velocity and the mass of each vehicle. If you start moving, each car will take less of a "hit" due to the differential velocity being lower. If you start moving before a collision, you might even avoid contact altogether. Of course, I am not an automobile safety expert, and you might actually cause a different accident if you try to move out of the way (hitting somebody else or someone).

SteveM