Green Line Extension

Green Line Extension (GLX)
A train on the Medford Branch in 2024
Overview
Owner	Massachusetts Bay Transportation Authority
Locale	Cambridge, Somerville, and Medford, Massachusetts
Termini	Union Square (D) Medford/​Tufts (E)
Stations	7 open, 1 proposed
Service
Type	Light rail
System	Green Line (MBTA subway)
History
Opened	March 21, 2022 (Union Square Branch) December 12, 2022 (Medford Branch)
Technical
Line length	4.3 miles (6.9 km)
Number of tracks	2
Track gauge	4 ft 8+1⁄2 in (1,435 mm) standard gauge
Electrification	Overhead line, 600 V DC[1]: 11.1-1
Operating speed	50 miles per hour (80 km/h)[1]: 1–5
Route map Legend  Lowell Line  Mystic Valley Parkway proposed Medford/​Tufts Ball Square Magoun Square Gilman Square East Somerville Union Square  Fitchburg Line  Maintenance Facility Lechmere closed 2020 Lechmere to North Station to Science Park This diagram: view talk edit

The Green Line Extension (GLX) was a construction project to extend the Massachusetts Bay Transportation Authority (MBTA) Green Line light rail system northwest into Somerville and Medford, two inner suburbs of Boston, Massachusetts. The project opened in two phases in 2022 at a total cost of $2.28 billion. Total ridership on the 4.3-mile (6.9 km) 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. 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. The project includes a 1.9-mile (3.1 km) extension of the Somerville Community Path to North Point.

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, while the Medford Branch opened on December 12, 2022. The Community Path extension opened in June 2023.