The Northeast Corridor (NEC) is an electrified railway line in the Northeast megalopolis of the United States. Owned primarily by Amtrak, it runs from Boston through New York City, Philadelphia, and Baltimore to Washington, D.C.. The NEC closely parallels Interstate 95 for most of its length, and is the busiest passenger rail line in the United States by ridership and service frequency as of 2013. Branches to Harrisburg, Pennsylvania, and Springfield, Massachusetts, though not considered part of the Northeast Corridor, see frequent service from routes that run largely on the corridor.