Haymarket North Extension

Haymarket North Extension

Company type	Rapid transit extension
Industry	Public transportation
Founded	1975–1977
Headquarters	Boston, Massachusetts , United States
Area served	Boston metropolitan area, Massachusetts
Products	Rapid transit service (Orange Line)

The Haymarket North Extension represents the northern portion of the Massachusetts Bay Transportation Authority's rapid transit Orange Line. It extends from North Station, passing beneath the Charles River, and follows the Haverhill Line corridor up to Oak Grove in Malden, Massachusetts. Constructed as a replacement for the Charlestown Elevated and originally intended to reach Reading, this extension was inaugurated between 1975 and 1977.

Route

Commencing just beyond Haymarket station in Boston, the extension features an underground stop at . It travels underneath the Charles River and emerges near Community College station in Charlestown. The track runs at grade beneath the elevated structure of Interstate 93, then crosses over both the Haverhill Line and Newburyport/Rockport Line via a flyover to arrive at Sullivan Square station. From Sullivan Square northward, the line runs adjacent to the western side of the Haverhill Line tracks, continuing at ground level through Assembly station in Somerville. It then traverses the Edward Dana Bridge over the Mystic River to reach Wellington station. Past Wellington, the route briefly tunnels beneath the former Medford Branch before ascending on an embankment into Malden. The elevated Malden Center station provides a connection to the Haverhill Line. The extension proceeds at surface level until terminating at Oak Grove.

The stations Sullivan Square, Wellington, and Malden Center function as significant bus hubs for northern suburban areas, facilitating transfers to MBTA bus routes serving communities such as Woburn, Reading, and Saugus.

Station listing

Station	Opening date	Notes
REDIRECT Template:Boston transportation system	March 20, 1977	Connection to Haverhill Line
REDIRECT Template:Boston transportation system	December 27, 1975	Connection to Haverhill Line
REDIRECT Template:Boston transportation system	September 6, 1975
REDIRECT Template:Boston transportation system	September 2, 2014	Infill station added post-original extension
REDIRECT Template:Boston transportation system	April 7, 1975	Replaced former elevated station
REDIRECT Template:Boston transportation system	April 7, 1975
REDIRECT Template:Boston transportation system	April 7, 1975	Substituted elevated station; reconstructed in 2005 as an underground "superstation" with Green Line connections

Architecture

Echoing the design approach of South Shore Line stations (the Braintree branch of the Red Line) constructed during the same period, original stations on the Haymarket North Extension exhibit a distinctive Brutalist aesthetic characterized by bold concrete geometries. Community College and Sullivan Square stations—situated beneath the I-93 viaduct—feature predominantly rectilinear architecture; subsequent stations introduced angled components accommodating stairways and elevators.

Planning

The Charlestown Elevated (El), unlike its counterpart the Washington Street Elevated, was positioned adjacent to Boston Harbor and near the Mystic River estuary, subjecting it to accelerated deterioration from salt air corrosion. Additionally, it faced criticism for generating noise and obstructing sunlight along Main Street. In 1965, to secure local backing for redevelopment efforts, Edward J. Logue pledged removal of this elevated structure. Given political opposition to maintaining an elevated line and prohibitive costs associated with a full tunnel, planners opted to utilize existing rights-of-way owned by the Boston and Maine Railroad (B&M), incorporating only limited tunneling. Construction commenced on September 22, 1966. Following deliberations, plans were finalized for the extension to end at Malden’s northern boundary rather than continuing into less densely populated suburbs such as Melrose and Wakefield.

In 1970, the MBTA proposed using dual-mode diesel-electric railcars (BIPED) capable of operating on commuter rail tracks beyond Oak Grove to provide through service between Boston and Reading. These adaptable vehicles were also intended for deployment on other lines including the Fitchburg Line past , as well as South Shore routes beyond . However, this concept was rejected by the state Department of Public Utilities due to safety concerns regarding possible electrical malfunctions igniting diesel fuel within downtown tunnels.

Construction

The tunnel beneath the Charles River was created using an immersed tube technique, where steel segments were submerged into a pre-dug trench and subsequently encased in concrete applied through a tremie. Sections of the tunnel on land were built using the cut-and-cover method, featuring a reinforced concrete box with walls measuring thick. Transition sections, which are long and have walls thick, serve as connectors between the underwater and land portions. Construction activities in Boston necessitated underpinning both North Station and the Central Artery/Leverett Circle highway bridge.

The Edward Dana Bridge spanning the Mystic River had a construction cost of $9.1 million. This structure consists of two parallel bridges: one carrying three rapid transit tracks and the other supporting a single track for commuter rail and freight traffic. Platforms were extended to accommodate six -long cars, an upgrade from the previous four-car length; following station alterations, six-car train operations commenced in 1987.

The Charlestown Elevated ceased operations on April 4, 1975, with the new segment from Haymarket to Sullivan opening on April 7 to directly replace it. North Station and Sullivan stations took over from nearby elevated stops; they replaced former and stations. The extension stretching from Sullivan across the Edward Dana Bridge to opened on September 6, 1975, including the establishment of the Wellington Shops for railcar maintenance, which succeeded Sullivan Square and later Forest Hills Shops. The section extending to elevated, featuring a platform for the Haverhill Line, began service on December 27, 1975. The terminal station opened on March 20, 1977.

The project's pace and expenses generated debate. The initial segment required eight and a half years to complete—twice the originally projected time—and cost $180 million, more than double initial estimates. In March 1975, Governor Michael Dukakis commented on these delays. MBTA officials pointed to several causes: B&M's refusal to grant full construction access until MBTA acquired the Western Route for $18 million (finalized in September 1973), relocation of B&M tracks, underpinning difficulties, and challenges faced by engineering consultants.

Reading plans and third track

Originally, plans called for extending service northward to , aiming to replace commuter rail operations between Boston and Reading. Without dedicated commuter rails on that stretch, all Haverhill trains would have been routed via the Lowell Line and Wildcat Branch, a path used from 1959 until service ended in 1976. When Haverhill service resumed in 1979, trains traveled through Reading; only certain rush-hour trains along with Amtrak's Downeaster continue to utilize the Wildcat Branch.

As part of the extension project, a third express track was constructed with the intention of supporting express services to Reading. This track was built running from just south of Community College station to just north of Wellington station. The engineering firm recommended this addition as a future-proofing measure; however, some officials suspected it inflated project costs to increase consulting fees. In September 1972, the MBTA announced that due to financial limitations beyond Oak Grove station, express service would not be implemented since time savings from Malden were minimal and the third track space was required for commuter rail operations. A General Accounting Office report from 1982 criticized MBTA's $2.3 million federal spending on this third track, though MBTA attributed the absence of express service to external political influences.

Currently, the third track is occasionally utilized for equipment testing and rerouting during severe weather conditions. In 2007, it was used for testing new Blue Line cars. During construction at Assembly station, outbound trains operated on this third track while inbound trains used the usual outbound track to allow for ongoing work.

Assembly station

In the early 2000s, Somerville initiated plans for the Assembly Square project on the site formerly occupied by the Somerville Assembly automobile factory. A major element of this development was the introduction of an infill station positioned between Sullivan Square and Wellington stations to encourage a reduction in automobile usage. Following a construction period lasting two years, Assembly station commenced operations on September 2, 2014. This marked the MBTA's first new subway station opening since 1987 and represented the first infill station added since Quincy Adams in 1983. Assembly station is designed with an island platform situated between two primary tracks; during the building phase, outbound trains operated on a typically unused third track, while inbound trains ran on the outbound track. The station's angular architectural style pays homage to the original Extension stations but incorporates contemporary design elements.