I don't know where you are coming from. If the empty train is 4,000 tons, the loaded train would weigh approximately 15,000 tons. This is a typical 110 car unit grain train. Clearly this would require considerably more locomotives than moving the 4,000 ton empty train over the pass! The grain business wouldn't be very efficient if the empty train weighs 4,000 tons and the loaded train only weighs 5,000 tons, you are only moving 1,000 tons of grain?