I should have been more clear. I was thinking more along the armor lines.
Simple collisions, no one has to die, just can't drive through and hide in the other. Kinda like hitting a building and stopping, that sorta thing. Friendly vehicle collisions should also be on.
Now that you guys brought it up, I see that it would need more research than I thought.
An M3 running into any tank at full speed might get catastrophic damage. M8 might lose a wheel or two and 'maybe' damage its main gun. I'm just guessing here.