Sorry, Jonathan, but there are tgd's which I'd rather keep to myself. With the hints and tgd's provided in this and other threads regarding roads and such, it would be possible to find out. If you can warp a narrow simple shape line, you can double that with a transform shader, or just add another line at 1.35m from the first. You'd have to make a mask for the sleepers, and one for the attachment (nuts+plate), which can be used with the same warper. Every bit can be merged (added or differenced...), and used for a color input and/or displacement.
I know about the greens. I'm always told I use too hard greens. Anyway, here's another one, probably final, as I'm getting fed up with it now. Up to something else.