In the late 1960s, the MBTA began work on the Haymarket North Extension project. It included a tunnel segment north from Haymarket through a new underground stop at North Station, then under the Charles River to a portal south of the Gilmore Bridge. From there, the extension was built along the Haverhill Line commuter rail right of way. Community College station was built to replace the two elevated stops nearby in Charlestown. The new route opened to Sullivan Square on April 7, 1975. The Main Line had previously been renamed as the Orange Line in 1967, as part of a systemwide rebranding by the newly formed MBTA.