Commuter trains are either powered by diesel-electric or electric locomotives, or else use self-propelled cars (some systems, such as the New York area's Metro-North Railroad, use both). A few systems, particularly around New York City, use electric power, supplied by a third rail and/or overhead catenary wire, which provides quicker acceleration, lower noise, and fewer air-quality issues. Philadelphia's SEPTA Regional Rail uses exclusively electric power, supplied by overhead catenary wire.
