Are you placing the roads by hand or are they being generated at runtime? If you are placing them all by hand I personally recommend, vertex painting an object into it’s surrounding world, either using the surrounding materials to blend onto the mesh or push the world position offset down into the surrounding meshes.
Some examples and resources:
https://www.youtube.com/watch?v=tyLSH5zF-rII know that’s kind of not really an answer but hopefully that’s enough to give you some ideas.