The Frederick Branch is a railroad line in Frederick County, Maryland. It was built by the Baltimore and Ohio Railroad (B&O) in 1831, and is now owned by the Maryland Department of Transportation (MDOT).[1] The 3.4 mi (5.5 km) branch extends between Frederick Junction – a wye with the Old Main Line Subdivision of CSX Transportation on the west side of the Monocacy River – and its terminus at East Street in downtown Frederick, Maryland. The wye at Frederick Junction was the first example of its kind in the United States[citation needed] and is still in use today.