This would be something for Badspot and co. to implement.
As is, vehicle-to-vehicle collisions are screwy as all hell. Cars get stuck on each other, go flying, and all sorts of other bad things. What to do? Simple. Don't make vehicle-to-vehicle collisions rely on complex physics. Just have them sort of "bump" away from each other in opposite directions. If you need an example, just look at any Mario Kart game.
