If I opened a dumped .obj mesh of a vanilla or workshop road in Blender, I only saw the vertices/points. But, if I opened the file with Windows 3D Builder (right clicked on the file and selected "3D Print" in the context menu) I could see the mesh.

Opening the file in 3D Builder and exporting as a .obj fixes the file. 3D Builder threw an error the first time I tried it, so I saved the road as a different file format first (.stl) and then the export to .obj worked. Textures are a mess though.