Yes you can - that's what Photoshop is for - after the event trash clean up and people remover!
Chris is right -- Photoshop can change reality. But if a photographer is to present the truth, the image needs to show the scene as it was, warts and all. Unfortunately, much of the railroad environment is treated as a trash pit, and attempts to show it as clean distorts that reality. If you want a "clean" image, get a painting, the result of "artistic license."