power of an electric locomotive. Overview of electrification in the U.S. Electrification in the US reached its maximum of in the late 1930s. By 1973 it was down to (Class I railroads) with the top 3 being: Penn Central , Milwaukee Road , Long Island Rail Road . In 2013 the only electrified lines hauling freight by electricity were three short line coal haulers (mine to power plant) and one switching railroad in Iowa. The total electrified route length of these four railroads is . While some freight trains run on parts of the electrified Northeast Corridor and on part of the adjacent Keystone Corridor, these freight trains use diesel locomotives for traction. The total electrified route length of these two corridors is . Diesel-powered freight runs similarly operate over the South Shore Line and the San Diego Trolley light rail system. Current systems Several additional heritage railways operate electric excursions on former main lines, including the East Troy Electric Railroad ( of tracks) and Western Railway Museum ( of tracks). History of electrification projects in the United States Smoke abatement Cleveland Union Terminals Co. In June 1929 this railroad switched from steam to electric operation on a route between Collinwood and Linndale in Ohio. A overhead system was used. This change of operation was for smoke abatement. Electric operation ceased in 1953. New York Central Railroad (Hudson and Harlem Divisions) The New York Central electrified a section of its main line Hudson Division route in 1913 from New York City (Grand Central Terminal) to Harmon (now Croton-Harmon), where it changed to at first steam, then diesel power. The Harlem Division in Westchester County, New York was also electrified to North White Plains. Metro-North Railroad, the successor to New York Central's commuter operations, continues to use these lines, and extended the Harlem Line electrification to Southeast in 1984. The lines are electrified at with under-running third rail. The Hudson Line is used by Amtrak for intercity passenger service to and via Albany, but these trains run to Penn Station via the Empire Connector, and only in the underground area in and near that station do Amtrak's dual-mode (diesel and electric) locomotives shift to using the overrunning DC third rail. Tunnels Baltimore and Ohio Railroad The construction of the Howard Street tunnel through Baltimore in order to make a rail connection to New York City brought about the world's first mainline