A key component of the layout are the two tunnels. I think I used a Bachmann 0n30 flat car to give me the set back of the side walls. These were made of scale 4 x 8 foot panels of 1/8 inch thick ply. The roof panels are just sitting there at the moment. The curve shown is not a uniform radius. I was lucky on this side, as mentioned previously, in not getting any kinks in the rails. By bending the rail to fit I also seemed to have got appropriate transitional curvature in. This probably helps with tracking.