I think that this is another screen. Here is my work so far with the different track tubes. If this is not clear enough, then I'll post a larger image on Nldc. As you can see the overbanks are 4 tube and so is the front and end of the first hill. If there is anywhere else you think needs 4 tube track post where here. I'm probably also not going to have any two tube track except for the area around the station. My track will need to be stronger than that in most places.
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Enjoy.