Haymarket North Extension

The Haymarket North Extension is a section of the Massachusetts Bay Transportation Authority's rapid transit Orange Line which currently constitutes the northern section of the line. It runs from North Station (MBTA station) through an underground crossing of the Charles River (with the 2003-completed Leonard Zakim Bridge later built directly over it), then along the Haverhill Line right-of-way to Oak Grove station in Malden, Massachusetts. Built to replace the Charlestown Elevated and originally intended to be extended as far as Reading, it opened in stages between 1975 and 1977.

Unlike the Washington Street Elevated (which was built as the same time and with a similar design), the Charlestown El was located very near Boston Harbor and the Mystic River tidal estuary, and was thus continually exposed to accelerated corrosion caused by salt air. The elevated was also unpopular with many local residents, as it was noisy and blocked out sunlight to Main Street. In the 1960s, it was determined that a replacement elevated would not be wise to build, and that a full-length replacement tunnel would be too expensive. Additionally, original plans to extend the El to Reading would never have been possible to realize, as the line would have run required an unpopular and thus politically infeasible elevated routing down Main Street through Malden, Melrose, Wakefield, and Reading. Instead, the Haymarket North Extension project was rerouted using existing railroad rights of way, plus limited use of tunnels.

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