Road decal problem

So here's the case: I just put some asphalt road on a map and then drove on it. This is what happened:



Soil and stones shouldn't be coming out, there should be smoke and better grip. Now I wonder, have I done anything wrong? Is there some sort of setting I need to change for the roads to have the proper behaviour?
Please help me with this!

 

You need to put concrete underneath the road by painting it on with the terrain texture

 

Thanks!​.........