Red Blue Connector

Red Blue Connector
Company type	Proposed transit infrastructure project
Industry	Public transportation
Founded	1991 (commitment as part of Big Dig)
Headquarters	Boston, United States
Area served	Boston, Massachusetts
Products	Subway line extension and connection
Website	www.mbta.com/projects/red-blue-connector

The Red Blue Connector represents a proposed MBTA initiative aimed at extending the Blue Line westward by 0.4 mi (0.64 km) from its current endpoint at Bowdoin station to a new terminal at Charles/MGH station, thereby establishing a direct link to the Red Line. This extension would result in the closure of Bowdoin station and alleviate congestion issues at Downtown Boston stations by creating a seamless connection between the two lines, which currently depend on transfers through the heavily crowded Green Line. The project intends to enhance transit accessibility for neighborhoods such as Cambridge and East Boston.

An underground link connecting the Blue and Red Lines has been under consideration since the 1920s but only gained significant attention in the 1970s. Development efforts stalled until 1991, when Massachusetts committed to constructing the connector as part of the Big Dig highway initiative. Despite this commitment, construction never commenced, and the project experienced a temporary halt between 2005 and 2006. Interest revived during the 2010s, leading to design progress reaching approximately 30% completion by 2024; however, funding for construction remains unavailable. The project's ongoing postponements have attracted criticism despite broad political endorsement and public approval.

Background

Among MBTA subway lines, only the Blue and Red Lines lack a direct connection; passengers are required to transfer via either the Green or Orange lines or walk roughly along Cambridge Street between Bowdoin and Charles/MGH stations.

The Green Line functions as the main transfer corridor between the Blue and Red Lines, resulting in significant overcrowding between Government Center and Park Street during peak periods, which causes notable delays. Presently, traveling from Government Center to Charles/MGH via the Green and Red Lines averages about 11 minutes. The proposed Blue-Red connector aims to reduce this travel time by roughly 4 minutes for riders.

Historical connection

In the early 1900s, before MBTA color coding was established, a physical rail link existed between what are now known as the Blue and Red Lines. Blue Line trains accessed a ramp near Bowdoin station and ran on non-powered streetcar tracks along Cambridge Street to connect close to Kendall/MIT station on the Red Line. This track was exclusively used for transferring Blue Line cars to maintenance facilities near Harvard Square and was never open for passenger use. Following the establishment of separate maintenance yards for the Blue Line, this connection was dismantled and the ramp sealed off in 1952.

Tunnel

The connector is intended to run as an underground tunnel beneath Cambridge Street entirely within Boston city limits. Construction techniques under consideration include cut-and-cover (C&C), sequential excavation method (SEM), and deep-bore tunneling using a tunnel boring machine (TBM). While initially planned as a cut-and-cover project, concerns about surface-level disruption shifted preference toward a deep-bore tunnel from 2010 until 2018, when plans reverted back to employing a shallow cut-and-cover tunnel approach.

Stations

By 2024, the initiative encompasses a single station: an underground platform on the Blue Line at Charles/MGH located beneath Cambridge Street, just east of the primary headhouse. This facility will facilitate seamless transfers between the Blue and Red lines within the fare-controlled area.

Bowdoin station is planned for closure due to high construction expenses and the potential for faster travel times. Although earlier concepts explored rebuilding or keeping Bowdoin operational, recent strategies designate it as a staging zone during construction activities.

Early planning

A 1924 investigation explored extending the East Boston Tunnel toward Charles Street. In 1926, a proposal sought to transform the Tremont Street subway and streetcar routes into rapid transit corridors by extending the East Boston Tunnel southward to Park Street, enabling continuous service between Maverick Square and Brighton along the Commonwealth Avenue line. Three route options were analyzed: one heading south from Bowdoin and two diverging southwest from a relocated Scollay Under.

From the 1940s through the early 1970s, regional plans prioritized suburban expansions without extending downtown beyond Bowdoin. By the mid-1970s, due to Kendall Square’s development, the Red Line extension to Alewife, and increased Logan Airport travel demand, a direct connection between the Red and Blue lines became justified. A 1974 state plan proposed an extension to Park Street; subsequent updates in 1978 and 1983 shifted attention toward Charles/MGH.

A 1986 MBTA feasibility study examined constructing a cut-and-cover tunnel west of Bowdoin Street while leaving Bowdoin station unchanged, estimating costs between $79 million and $95 million (in 1986 dollars). A 1987 cost-effectiveness report predicted approximately 9,030 daily one-way riders on this extension.

Big Dig

In 1991, as part of an agreement addressing auto emissions from the Big Dig, the state committed to several transit projects including the Red Line–Blue Line connector, initially planned for completion by 2011. The Charles/MGH station reconstruction (2003–2007) was designed with provisions for a future Blue Line platform east of the existing headhouse. Nevertheless, in 2005, the connector project was postponed to prioritize other air quality initiatives. After another lawsuit by CLF in 2006, the state agreed to finalize the connector’s design.

The 2010 Draft Environmental Impact Report (DEIR) proposed constructing deeper tunnels using a tunnel boring machine (TBM) beginning east of Bowdoin station beneath its current platform. Options included relocating Bowdoin station west of Bowdoin Street or closing it entirely—the latter was favored due to lower costs and improved travel times. Maintaining Bowdoin station and its loop was rejected because evacuating passengers from a disabled train within the tight loop would be unfeasible, and the eastbound platform could not handle six-car trains. Employing a TBM rather than cut-and-cover methods aimed to reduce expenses and limit disruption along Cambridge Street.

Due to funding shortages, the MBTA did not complete design or construction phases. In 2013, a public-private partnership (P3) was explored to advance progress on the project. By 2015, the EPA lifted MBTA’s obligation to complete design work for this connector.

Project redesign

In 2018, a state-funded study valued at $50,000 reassessed tunneling approaches and associated expenses, revealing that cut-and-cover tunneling might prove substantially more cost-effective than a tunnel boring machine (TBM), albeit with increased surface-level disturbances. The projected expense for cut-and-cover tunneling was estimated between $200 million and $250 million solely for the tunnel, whereas TBM costs ranged from $300 million to $350 million, both figures falling below the $413 million projected in the 2010 Draft Environmental Impact Report (DEIR). Additionally, the MBTA’s June 2018 long-term plan suggested constructing a pedestrian passage connecting Orange Line platforms at State and Downtown Crossing stations to improve Red and Blue Line transfers, analogous to the Winter Street Concourse. In both 2019 and 2023, the MBTA allocated $15 million within a five-year framework dedicated to designing this connector.

By 2020, conceptual plans favored employing cut-and-cover methods coupled with the closure of Bowdoin station. The envisioned Blue Line platform at Charles/MGH would be accessible through the current lobby and an adjacent Massachusetts General Hospital (MGH) development. The overall project budget was projected at $850 million, encompassing $740 million for construction (including a 30% contingency), $50 million for design efforts, $30 million for administrative costs, and an additional $30 million allocated for new rolling stock. Construction was anticipated to occur between 2025 and 2030. A Notice of Project Change was released in October 2023, followed by a directive from the Massachusetts Executive Office of Energy and Environmental Affairs in November 2023 requiring a Supplemental Draft Environmental Impact Report.

Currently, $30 million has been designated to complete approximately 30% of design work and environmental assessments. As of June 2024, financing to support full project design and construction has not yet been secured.

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