Creating tunnels

[Railhead001]

I managed to find a tunnel spline that I like but never made tunnerls before. How do you build a mountian over the spline without the tracks moving along with tha land or is there another approach in doing so ?
Any help greatly appreciated.

RH001

 

[oknotsen]

Simply give one of the two spline points a set height. From that moment on it will ignore the land and just form a straight line between spline points.

 

[llebrez]

To expand on it, once you have the spline buried down there, you can add splines so you can bend it and make unbelievable things. Make the grid transparent so you can see "inside down there". More elaborate? flatten the mountain so you can manipulate in detail adding signs (in my case even turnouts and sidings), then re-do the mountain over it. Things that tunnel engineers would only dream, we can do in Trainz with a few clicks.