Problem with tunnels are that they are within the terrain and anything to do with terrain, the game logic will get touchy and kept raising terrain collision error.
I plan to dig some holes in the terrain to get around that error, it will take ages to work out the parameters surrounding the tunnel entrance which have an invisible no touch zone around it.
The maximum depth I can dig into is 11.9 below surface level in one placement of the mod on the surface. (I test it with a completely flat map from here https://www.transportfever.net/filebase/index.php/Entry/2430-Flat-Map-Pack-V-1-1/)
Beyond 11.9 meters the game will produce a "Unable to align terrain" error.
Using the noise barrier in game to cover the deformity inside
The menu is just a mock up (borrow from fly junction ), when I get the time to develop this mod, the options on the menu should be WAY LESS, curves may not be included...
I don't think I can live without this ruler from now on ! the distance the track can get closest to tunnel entrance is 16 meters. Ruler @ Maßstab
The terrain need to retreat 6m before showing an open tunnel (without tunnel collapse), many failed attempts at the background
The tunnel still collapse when you have many tracks entering the tunnel at -11.9 meters below the surface.
When I start trying to make the double tracks version of going down to a tunnel, I can't seems to make it work, Terrain Alignment Collision
For now my conclusion for this mod is that it requires absolutely flat ground to work. It is very rigid and may not be helpful