Making models react to truck tyre collisions?

[Digital X]

I've been away for a while and getting back into the Blender side of things, I wanted to make a gravel road but have the stones react to the tyres in such a way the weight of the truck (or tyre collision) would push them out the way dynamically as it would if you were to drive over stones in real life. The closest I have gotten is making a road with a Displace modifier using a Displace texture, but it's not the same as actual stones reacting.

I've loaded in a sign and noticed in its collision box properties it has a mass of 1.0, I can knock the sign over in the map editor, but once it's on the ground it doesn't seem to react any further. I cannot see any physics applied in Blender either.

Is it possible to do this with a large amount of small stones?