Hello PrinceOfPluto,
Figured I'd start a discussion here rather than clog up your comment section.

With regard to your question:

do you happen to how to modify the RoadDef curve data to make a caravan encounter map on a rail tile generate strictly vertical or horizontal road terrain? If a train caravan gets attacked, I'm hoping to have it generate a map with road terrain that allows the train to actually path to the map edge so that the game allows it to properly exit the map. If there's not a way to define that in a RoadDef, I'll probably end up having to do some Harmony patches that modify the encounter map after it generates.

I know the two locations you can start with:
1. Textures\Terrain\Surfaces (various texture files)
2. (Mod Steam ID # Folder) \ (Rimworld version) \ Defs\TerrainDefs\Terrain_Road (xml file)

I've been working on a new train mod that uses the upcoming Vehicle Framework from SmashPhil to have trains require rail terrain to move about on the colony map and "rail" tagged roads to travel on the world map.

By the way, that sounds absolutely fantastic. Very, very exciting. If it's something I need to do on my end in the C# or xml code for RRotR let me know, I'd be very happy to add it in.