Extending Green Line service to Cambridge, Somerville, and Medford has been the subject of several studies over the last 40 years.  One of the objectives of the 1962 North Terminal Area Study was to “design a new transit alignment to permit a future branch extension (of the Green Line) to Somerville and communities northwest along the right-of-way of the Boston and Maine Railroad.”  The 1973 Boston Transportation Planning Review Northwest Study focused on identifying and evaluating various bus, commuter rail, and Green Line extension alternatives in the “Somerville Radial Corridor.”  In 1981, the MBTA conducted the Green Line Northwest Project Study, which evaluated transit alternatives beyond Lechmere Station.

Documents related to the history of the Green Line Extension Project can be found at the State Transportation Library.

In early 2005, a Major Investment Study/Alternatives Analysis (MIS/AA) was prepared by the MBTA (available for download from the Document Archive) to define the most appropriate transit investment strategy for improving mobility and regional access for residents in Cambridge, Somerville, and Medford.  Although the MIS/AA did not identify a preferred alternative, the SIP identifies the mode and appropriate terminus for the project.

On October 2, 2006, EOT submitted an Expanded Environmental Notification Form  to the Secretary of the Executive Office of Environmental Affairs for an extension of the MBTA Green Line to Somerville and Medford.  Public comment for the project was received for eight weeks from the initial filing - including at public meetings in Somerville and Medford - after which the Secretary of EOEA issued a certificate requiring the preparation of a Draft Environmental Impact Report.