Like many of the symbols in Ethan Frome the farm, the sawmill, and the railroad show Ethan their most sinister aspects, expressing the anxiety of an early 20th century people moving away from rural, agricultural society and toward an urban, industrial one.
The sawmill, a machine that processes wood for a variety of uses, stands in stark opposition to the natural beauty around it. Ethan, with his deep love for nature seems an unlikely mill operator, which is probably a factor in his lack of success with it. When he, a man that makes his living by cutting down tries, tries to kill himself and his lover by colliding with a tree, a deep environmental anxiety is being expressed.
The railroad is a symbol of progress, movement, change, and modernity. For Ethan and other residents of Starkfield, the train symbolizes just the opposite. It signals their stagnation, their backward slide into deeper economic miseries. Because the train can now take people from the surrounding areas into the larger town and cities, nobody stops in Starkfield to do business, to make a purchase, or to visit. As such, Ethan's farm and mill aren't worth enough to sell. He can't sell, and he can't save. He's trapped by a technology that has left him in its dust.