Tonight's your night, buddy!
Hey there Viperman...
Here's a plan I just threw down a couple minutes ago. I haven't read through all the more recent posts and it's been a little while since you PM'd me (back in september!) but here 'tis, better late than never, I guess, since you're still at the foam board stage.
OKAY...here goes. I should begin by saying that it is by far complete...that is, there is more room for sidings and other industries, although I personally would not fill the whole space with rail-served structures, but that's just me.
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Siding A is an interchange track. Your lone GP40-2 heads out from over near the wye around the back side of the layout across the 90 degree crossing and picks up the cars left there. Then the set-outs and pick-ups begin. Industry C...I'm thinking PikeStuff 'metal' industrial building with loading doors for a couple 40' hi-cube boxes. Whatever they make there, requires a covered walkway over the tracks. I remember an industry near me in La Mirada (Buena Park, actually) that had a structure like that over the BNSF main line into LA.
Industry B...I'm thinking scrap yard...or recycling center, with front-end loaders and a crusher/conveyor, old-boxcar office building, fence made from old boxcar sides, etc. 40 and 50' gons get shoved in there loaded and hauled out empty, or vice versa if trucks haul in the stuff rather than haul it out.
The structure in the wye is your interlocking tower, still in use, but mostly as a crew change point. The loco could remain parked on either the curved or straight section along the right of the benchwork. For local work like this, I'd even get a heavily grafitti'd caboose. Something like the TRIX UP wide vision.
The section to the left on the other side of the scenic sky divider (just painted basic sky blue...unless you can find some cool photo backdrops to set your scene) is for your 4 foot bridge. If this is set in the SW somewhere, I'd make it a bridge over a dry wash, possibly with cattle grazing in the shade (too bad they can't be animated to jump up and run whenever your train rolled through! There was one spot near Tehachapi...you'd think they'd learn after a while!) Anyway, not sure what sort of bridge you've got, but that'd determine what kind of scenery goes beneath it.
No grades, all curves 18" radius except the siding A, which is drawn with 20", but shifted a 1/2" or so from the inner curve for clearance. Turnouts are #4 or 18" rad. snap track. I'd go with #4's and trim to fit. The crossing on the far right near the interlocking tower is close to a 45 deg., but you may have to fiddle with the location of the turnouts on the curve of the wye to make that line up exactly.
Okay...lemme know what you think and give me some more industry ideas so I can fill in any additional sidings you think it needs. So far you're running gons and hi-cube boxes...what else would you like to see? Pick industries that fit those types of cars. If you're going modern, I'm thinking some of those nice black cargill corn syrup tankers, and perhaps an industry that takes plastic pellets in covered hoppers. With such tight curves I'd stay away from center-beam flats and autoracks, long stuff like that. 50' gons are gonna be tight but workable, along with any long box cars (like the ubiquitous RailBox cars).
Galen