Yeah, tunneling sux in this game as well as other things. I’m guessing you generated a map with hills or you went with flat and still got hills. Another part of this wonderful game that’s not right.
I don’t know if you seen me mention this before but someone on the German site posted about the height map this game uses when generating maps. Since the game is like it is, I try to get as little hills as I can and changing this one little file does the trick.
If you change this file, res\textures\terrain\ridge.tga, to all black, you’ll have flatter maps so less need to build tunnels and long bridges. You have to use something other than paint if you want to do it or just download this one – Gebirgsfreie Landschaften