The Navajo Mine Railroad operates between the Four Corners Generating Station and BHP's Navajo Coal Mine in New Mexico. The line started operation in 1974 using diesel locomotives and was electrified in 1984 because diesel operation was too expensive with the increasing train loads, fuel prices and problems with clogged oil bath filters on the diesel locomotives due to the excessive coal dust. Electrification is at overhead line. The railroad does not have any connection to the rest of the American rail network.