The project includes the design and construction of two branches of the existing Green Line: a main line branch which will operate within the existing MBTA Lowell Line’s right-of-way, running south of the relocated Lechmere Station in Cambridge to Medford; and a 1.4km branch line operating in the existing MBTA Fitchburg Line right-of-way to Union Square in Somerville. Seven new stations will be constructed as part of the project, including Lechmere, as well as associated electrical and signalling systems, and a new rolling stock depot.

MBTA intends to enter into a design-build contract with the best-value design-build entity that will be identified through a two-phase selection process, which includes a request for qualifications and a subsequent request for proposals.

Work will include design and construction of stations, bridges, retaining walls, a community path, a vehicle maintenance facility, tracks, signalling, power and other rail facilities. The project will also include testing and commissioning.

The contract is worth approximately $US 1bn, with the complete project estimated at $US 2.4bn, with funding coming from local, state and federal funds. The Federal Transit Administration pledged $US 996m through its New Start Engineering Programme for the project in December 2014.

MBTA began work on the extension's right-of-way in March 2013, marking the first major expansion of its light rail system after years of numerous false starts and political indecision.

MBTA will host a pre-procurement forum for the project on November 16 at the Park Plaza hotel in Boston.