I found the LOD Groups section in the Road settings and set it to active. It seems to work and builds the LOD models so that is good. Each road piece is treated as a complete object so it's necessary to break a road into separate segments using connection objects. Is there another way to break roads into separate LOD chunks? The custom prefab editor looks like it would be perfect for adding some traffic flow information. If there were a way to extend this editor that would be great. BTW - It looks like there's no support for undo/redo is that right?