Harold Interlocking is a large railroad junction in New York City. The busiest rail junction in the United States,[1] it serves trains on Amtrak's Northeast Corridor and the Long Island Rail Road's Main Line and Port Washington Branch, which diverge at the junction.
Reconstruction work on Harold Interlocking started in 2009, as part of the East Side Access project to bring LIRR service to a new station under Grand Central Terminal. As part of the project, two tunnels for Northeast Corridor trains to bypass Harold Interlocking were built to reduce congestion and accidents.