Jabarkan Green Line dari Massachusetts Bay Transportation Authority

The Green Line Extension (GLX) is a project to extend the Green Line northwest into Somerville and Medford. The project is opening in two phases in 2022 at a total cost of $2.28 billion. Total ridership on the  extension is estimated to reach 45,000 one-way trips per day in 2030. The project begins at the north end of the Lechmere Viaduct, where the former ground-level Lechmere station was replaced by an elevated station on an extended viaduct. The two branches split north of Lechmere, with the Union Square Branch following the MBTA Commuter Rail Fitchburg Line right of way to Union Square station in Somerville. The Medford Branch follows the Lowell Line right-of-way to Medford/Tufts station with four intermediate stations. A new vehicle maintenance facility and storage yard is located in the Inner Belt District.

An extension of service beyond Lechmere was considered as early as 1922, with the first formal proposal in 1926. Despite appearing in other regional plans throughout the 20th century, the state did not commit to the project until 1990. Planning began in 2006 with a projected completion date of 2014; this was delayed to 2015, then to 2018. A groundbreaking was held in 2012, with several early construction elements over the next two years. The federal government committed $996 million of the $2.2 billion cost in 2014.

In 2015, with projected costs increased to $3.3 billion, the project was placed on hold. A revised plan, with more modest stations and other value engineering, was submitted in 2016 and approved in 2017. The main $1.08 billion design-build contract was issued in November 2017, with several optional items like platform canopies and a larger vehicle maintenance facility included. Construction began in 2018, with the old Lechmere station closed in May 2020. The new Lechmere station and Union Square Branch opened on March 21, 2022, with the Medford Branch expected to open in November 2022.

Another mitigation project in the initial settlement was restoration of service on the E branch between Heath Street and Arborway/Forest Hills. A revised settlement agreement resulted in the substitution of other projects with similar air quality benefits. The state Executive Office of Transportation promised to consider other transit enhancements in the Arborway corridor.