Metro-North’s mangled and much-maligned service in Connecticut is made all the more challenging by a technological quirk of fate. Ours is the only commuter railroad in the U.S. that operates on three modes of power ... AC, DC and diesel.
On a typical run from, say, New Haven to Grand Central, the first part of the journey is done “under the wire,” the trains being powered by 13,000 volt AC overhead wires, or catenaries. Around Pelham, in Westchester County, the conversion is made to 660 volt DC third rail power for the rest of the trip into New York. Even diesel trains must convert to third-rail as their smoky exhaust is banned in the Park Avenue tunnels.