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seriously, most plastic models are a form of styrene, very easily recycled. Check with your recycler to see if it is compatible. Remove the metal axles, weights, couplers, etc. (always recycle Kadees!!!)
layout level recycling: flatcars are often used as rural bridges. Tankcars are fuel storage tanks on many ranches or diesel fueling stations. Boxcars are great for hay storage. Small closed hoppers are common as sand storage in diesel fueling facilities.
That reminds me, where I used to go to school, there was an old siding or something that used to run through what is now a giant U of Minnesota center, and their is some crane and excavating company that owns a farm or something. There was a few old boxcars sitting around for storage.
I like to take the trashy rolling stock and use them for everything from demonstrating weathering to creating graffiti cars. Very heavily weathered and with trashed (or removed) trucks, they also can make great yard offices.