Creating roads auto aligned to mesh or elevation image

I have a mesh in Blender (and an elevation map from it) and would like to use it to trace roads ontop of it. However, no matter what or how i import different files, Roadrunner ignores its shape and places roads under it. This can be fixed with the elevation map and the button to "Project roads" but this is highly inefficient, especially if i want to trace a lot of roads with intersections and tunnels. Just to give an idea, my mesh terrain is about 16x16 kilometers. Its not a super dense roadnetwork but loads of intersections and mountain-esk terrain. Projecting the roads and hoping for the best is not something i want to deal with at all.

Is there a way to draw roads ontop of anything? Preferrably an fbx mesh used as terrain/ground, since creating elevation images and point clouds from meshes reduces visual fidelity.