The New York, New Haven and Hartford Railroad completed electrification in 1907 of its New Haven–New York City mainline and was one of the pioneers of heavy electric railway use in the United States. The New Haven chose the system, later used by the PRR, in addition to working with Westinghouse to develop AC/DC electric motors (locomotives) to run on both AC overhead lines and DC third rail. The main line, now Metro-North Railroad's New Haven Line, was converted to in 1985.