I checked that out before. The road lines are customized polylines which means they can't be sculpted like a room with the Terrain Generator, so unfortunately not a solution.

The best way remains a room for roads, rivers, borders, etc. And if the road line must be a dotted/broken line my line objects will have to do. So far I needed that only in one place and that project is no longer in use.

Most roads I now use have borders but no center line and are separated by a wider piece of ground, mainly to avoid the line problem. My wish for rooms-between-rooms is mostly for rivers, borders, and walking paths. Also to construct parts of the terrain itself to fill in between created rooms.