Took this photo Sunday of a passenger train going east (locomotive is in the rear) along the former SP, now UP, route along Carquinez Strait between Crockett and Martinez, California:
That would be an interesting effect to try to model.
Maybe a shelf railroad under a valence. Stuff the valence full of fluffed-out cotton with some LED light strings behind it. Then a dry ice in water mist generator and a small fan to waft it across the scene?
Chuck (Modeling Central Japan in September, 1964 - with none of the above)