The whole terrain is a mesh, the roads (and other elements) are different tiles within that mesh.
It is made up of 256 meshes (16x16), each mesh is 32x32 quads, each quad 4units². Each 4unit quad has a 256x256 texture on it which effectivly gives you a detail level of 131072 x 131072 pixels.
The whole thing is vertex coloured by the texture, so it's not actually a texture as such.
The bizarre thing when you're working to scale means that every pixel on the textures on the terrain is in reality 1.5cm²
This screenshot will probably make it clearer
It is made up of 256 meshes (16x16), each mesh is 32x32 quads, each quad 4units². Each 4unit quad has a 256x256 texture on it which effectivly gives you a detail level of 131072 x 131072 pixels.
The whole thing is vertex coloured by the texture, so it's not actually a texture as such.
The bizarre thing when you're working to scale means that every pixel on the textures on the terrain is in reality 1.5cm²
This screenshot will probably make it clearer