Like in Spawntown? It is possible. My idea was for each region to have their own, unique walls for the rails. In Spawntown it's sandstone and bricks, so maybe you could combine sandstone with another material.
This was my idea for the rails in Epicland. You can make a proposal for how the walls and floors should be in the rail tunnels in Kaeshar.
Hmm, maybe all planks would actually look much better...
The idea with the plans is also to make the rails reflect the building style in the region, so the reason Spawntown has sandstone and bricks is because the buildings use those materials.