Railroads are a great source of abstract photos. This one was caught on the move; you can tell by the blurred grass on the far side.
Everything on a train is there because it’s supposed to be there. There’s very little decoration, it’s all working mechanical parts, which make for great abstracts. For a tutorial on abstract photography, check out my post from Monday. Basically, you are making the compositional elements prominent and reducing the realistic elements. Railroads and other industrial settings are great in the sense that these purpose-built machines are very simple in their design. Large solid parts, little detail or at least consistent repeating details.