The Union Railroad (reporting mark URR) is a Class III switching railroad located in Allegheny County in Western Pennsylvania. The company is owned by Transtar, Inc., which is itself a subsidiary of USS Corp, more popularly known as United States Steel. The railroad's primary customers are the three plants of the USS Mon Valley Works, the USS Edgar Thomson Steel Works (blast furnaces, basic oxygen steelmaking, and continuous slab casting), the USS Irvin Works (hot and cold rolling mills and finishing lines) and the USS Clairton Works (producer of coke for blast furnace ironmaking).