Okay, Oskar, here goes nuthin'. I've broken these sprites down as per the option 2 you mentioned yesterday. Honestly, I'm glad that you chose this method, because I was messing around with the other option last night, and there just wasn't enough depth to the tunnels. I mean, if you think about it, before the tracks in the tunnel disappear, they're only a couple pixels from the rail passing overhead. The illusion is then destroyed. But, with being able to draw shadows on the tunnel rails, they appear to be further below.
I do like the idea of the tunnel graphics changing over time. In fact, the old rusty trestle I drew would work well for, say, 1920's-1950's. Then, as the monorails and maglevs come into play, the other graphics can be used. Just wondering: would it be possible to randomize the later graphics? That way when a tunnel is build, one of the three other graphics would be chosen. It would add variability, and, if the player wants a particular tunnel graphic they can dynamite until the one they want is drawn. Just a thought.

I didn't know that there were so many sets that changed the rail graphics. No small feat to draw all of the variations. Especially considering that there are also three other land tiles, besides temperate, that I have to draw. Sheesh!
I do hope that the tunnels I drew work out okay. If something is messed up, let me know, and I'll try to fix it. Good luck!