Ah, great, Casper, but the rounded UK-style tunnels won't work well with my routes, which are Japanese. Most of the tunnels are square with perhaps cement portals. I am forced to use the Beton-type tunnels only because they have internal catenary. But (at least on my system) the portals are solid white and just look terrible. Plus, they are round also.
I wish I was good at creating content, or at least able to modify tunnels to add catenary to them. As a test, I put down catenary alongside the buried tunnel and then lowered each vertex down into the mountain until the arm showed inside the tunnel. Talk about tedious!
At the moment, as al alternative to the Beton tunnels, I've put down simple, square tunnels and ignored the fact they didn't have catenary inside them.
Bill