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1 `B' TRAIN: A TRACTOR pulling two SEMI TRAILERS. The lead unit having a FIFTH WHEEL at the back to attach the second SEMI TRAILER or PUP. (For photo: See `RIG'.)  BACKHOE: A, farm tractor with an EXCAVATOR on the back, and, usually, a bucket, front end loader, on the front.
A unit train (sometimes called a block train) is a train hauling freight of the same type. These are shipped to the same destination without being split. Recently the number of unit trains carrying Bakken Crude oil in DOT-111 tank cars have increased exponentially along the rail-lines leading out of North Dakota.