North–South Rail Link

North–South Rail Link
Company type	Planned infrastructure project
Industry	Rail transport
Headquarters	Boston, United States
Area served	Boston metropolitan area, northern suburbs, New Hampshire, Maine
Products	Rail tunnel connection between North Station and South Station

The North–South Rail Link (NSRL) is a planned tunnel or series of tunnels designed to connect North Station and South Station in the heart of Boston, Massachusetts. Its purpose is to create a seamless connection between rail systems serving the northern suburbs, as well as New Hampshire and Maine, with the broader national rail network. The initiative includes building new subterranean stations adjacent to the current ones, constructing approximately of tunnels, and adding further links to surface rail lines.

This project would merge Amtrak and MBTA Commuter Rail services that currently terminate separately at North and South Stations. For the MBTA network, it would enable northern lines to access South Station, Back Bay Station, and beyond, including routes such as the Framingham/Worcester Line and the Northeast Corridor. One alternative also proposes connecting southern commuter rail lines. The NSRL would also consolidate Amtrak operations by linking services like the Downeaster from Maine, which presently lacks a direct connection to Northeast Corridor trains bound for New York City.

A 2017 analysis by Harvard Kennedy School estimated the NSRL’s cost between $4 billion and $6 billion (in 2025 dollars), drawing on Federal Transit Administration figures and international tunnel project comparisons. Meanwhile, a 2018 MassDOT report outlined four potential designs with projected expenses ranging from $12 billion up to $22 billion (in 2028 dollars).

Currently, the NSRL remains inactive in terms of development; however, proponents continue advocating for renewed feasibility assessments.

Historical connections

Between 1872 and 1969, the Union Freight Railroad, dedicated solely to freight, operated as a street-level connector linking most railroads on Boston’s south and north sides, servicing local industries and docks.

From 1901 until 1938, the Atlantic Avenue Elevated provided passenger service directly bypassing both North and South Stations. Although elevated, its tracks were not physically linked to standard railroad lines.

Today, the western portion of the Grand Junction Railroad stands as the only existing rail link bridging Boston’s north and south railroad systems.

Present connections

Currently, public transit connects North Station and South Station only through indirect routes involving two MBTA Subway transfer points. Traveling between these commuter rail terminals requires using two subway lines—either switching between the Green Line and Red Line at Park Street station, or transferring from the Orange Line to the Red Line at Downtown Crossing station. Alternatively, passengers may opt for a walk lasting 20 to 30 minutes. Amtrak recommends taxi use for travelers with small children or heavy baggage.

Although direct travel across this divide is feasible on the Orange Line from Back Bay Station to North Station, it requires passing through seven stops; only four southern commuter lines serve Back Bay. The Orange Line also facilitates transfers for Amtrak riders moving between the Northeast Corridor and the Downeaster, yet North Station users contribute to congestion on this line. Likewise, South Station connects via the Red Line at Porter station to the Fitchburg Line. Passengers using the Newburyport/Rockport Line can transfer via the Silver Line from Chelsea. Additionally, weekday service by MBTA bus #4 links these two stations. The proposed North–South Rail Link seeks to replace these indirect transfers with direct rail service connecting both stations without intermediate changes.

2018 NSRL feasibility study

In June 2018, MassDOT published the North South Rail Link Feasibility Reassessment, which outlined multiple tunnel alternatives. The state initiated a $2 million feasibility study starting March 1, 2017, prompted by the North-South Rail Link Working Group. This coalition includes Senator Ed Markey, Representatives Niki Tsongas, Katherine Clark, and leader Seth Moulton, along with more than half of Massachusetts' mayors.

Options

The 2018 report analyzed four distinct options, with costs calculated in 2028 dollars. These estimates incorporated rolling stock acquisitions, infrastructure upgrades, and an assumed annual inflation rate of 3.5%. The projected South Station expansion carries a price tag of approximately $4.7 billion, excluding expenses for rolling stock procurement, electrification efforts, and renovations to Tower 1.

Two proposals involve tunneling beneath the Central Artery (I-93)—one featuring two tracks and another more expensive version with four tracks. The remaining two options suggest two-track tunnels located several blocks west of the Artery under downtown Boston. Each alternative would link northern commuter rail lines to South Station and continue toward Back Bay and western routes. Only the four-track configuration offers a connection from North Station to the Fairmount Line south of South Station. In all scenarios, the Old Colony main line services (Greenbush, Kingston, Fall River/New Bedford) would continue terminating at South Station’s surface platforms. Additionally, the existing North Station surface platforms could be removed under every option, enabling redevelopment opportunities on that land.

Central Artery four-track

The most extensive plan includes a new Central station (Union Station) positioned mid-route and a rail tunnel connection to the Fairmount Line. North Station would be relocated underground near its current location. Construction would require two TBM tunnels at significant depth combined with cut-and-cover methods in Fort Point Channel. An underground South Station is proposed east of the existing surface station within Fort Point Channel. Central station would provide a transfer to the Blue Line at Aquarium station, marking the Blue Line’s inaugural direct commuter rail connection. The estimated cost stands at $21.491 billion.

Central Artery two-track

This option mirrors the Central Artery four-track route but excludes the Central station. It consists of a single TBM tunnel constructed at considerable depth with cut-and-cover sections in Fort Point Channel. The underground South Station would be located east of the current surface station within Fort Point Channel. Estimated expenses total $12.317 billion.

South/Congress alignment

North Station would be completely underground and shifted several blocks south between State and Haymarket Streets, without a Central station included. Tracks and platforms would be vertically stacked inside a single TBM tunnel at substantial depth. An underground South Station would be situated northwest of the surface station location. This option’s estimated cost is $13.181 billion.

Pearl/Congress alignment

Similarly, North Station would be fully subterranean and relocated southward between State and Haymarket Streets, with no Central station planned. Tracks would run through two separate TBM tunnels at notable depths. The underground South Station would lie north of the surface station site. The projected cost for this alignment is $14.388 billion.

Electrification

Since diesel locomotives cannot operate within the tunnels, the use of dual-mode engines or the electrification of MBTA commuter rail lines is required. Although comprehensive electrification could enhance service dependability, shorten travel durations, and advance greenhouse gas reduction objectives, the 2018 plans propose only limited electrification. Partial electrification on the Fairmount Line would allow Amtrak and MBTA Northeast Corridor trains to reach South Station during construction at the Back Bay portal. Furthermore, the electrified infrastructure supports the South Coast Rail Phase II initiative, which aims to extend electric train service to Fall River and New Bedford.

Benefits

According to the 2018 feasibility analysis, implementing two-track configurations would raise daily ridership to 195,000 by 2040, compared to 150,000 under a no-build scenario. Enhancing all-day peak service could increase boardings further to 225,000, surpassing the 195,000 figure expected with only South Station expansion. Overall, the NSRL project would augment commuter rail capacity into downtown Boston by approximately 25%.

The study predicts morning commuter distribution from northern origins in 2040 under two-track scenarios as follows:

NSRL Estimated Morning Trips From Northern Directions in 2040, Two-Track
Destination	Passengers	Percentage
North Station	18,182	67%
South Station	5,477	20.2%
Back Bay	2,712	10%
Through service	771	2.8%
Total	27,142	100%

Potential challenges

The 2018 feasibility report identified significant risks associated with NSRL development. Construction of the tunnel portal at Back Bay would interrupt MBTA Worcester Line and Amtrak Lake Shore Limited operations, necessitating train terminations west of Back Bay or rerouting via the Grand Junction Line into North Station. Additionally, certain Amtrak services as well as Providence, Stoughton, and Franklin Line trains might be redirected through the Fairmount Line into South Station.

The plan anticipates substantial improvements in passenger boarding and alighting efficiency along with high train frequencies—up to 17 trains per hour per direction on two-track layouts—exceeding current Red Line levels and previous heavy rail systems equipped with positive train control. Achieving this frequency requires precise train scheduling and arrivals. Nonetheless, heavy rail systems such as London’s Thameslink have successfully operated up to 24 trains per hour.

With NSRL in place, MBTA commuter rail would become highly reliant on tunnel routes, increasing system-wide vulnerability to service interruptions. Although the design exceeds NFPA 130 life safety criteria, evacuating passengers from deep tunnels and stations remains a complex challenge. Deep station designs also result in longer access times for riders; for context, Porter Square is presently MBTA’s deepest station at a depth of 105 feet.

Early proposals

Various earlier efforts sought to establish a rail connection between South and North Stations. In 1987, Congress allocated funds for this link within a transit bill that was subsequently vetoed by President Reagan. The initial Big Dig project included an NSRL component but was later abandoned by the Dukakis Administration.

A prior concept known as the "Dorchester Avenue Alignment" bore resemblance to the four-track Central Artery alignment proposed in 2018. This plan featured two deep-bore tunnels approximately 41 feet in diameter extending beneath Boston beyond existing rail yards. The tunnels would run roughly 20 feet below the I-90 extension and reach depths up to about 130 feet at proposed Central and North Stations. Designed to carry four tracks with steep grades nearing three percent over nearly a mile in length.

Three portals were planned for connections southward to Back Bay station, Old Colony main line, and Fairmount Line; northbound portals would connect with the Fitchburg Line and other routes after crossing beneath the Charles River at approximately seventy feet below water level. The proposal included constructing two or three new underground stations near or beneath existing North and South Stations along with a potential Central Station close to Aquarium Station featuring platforms ranging between 800 and 1,050 feet.

Because pilings supporting South Station Tower complicated tunneling directly underneath South Station itself, track alignments would shift eastward with an underground facility situated roughly one hundred feet below Fort Point Channel near Summer Street. Tracks here would maintain a gentle slope of approximately 0.61%.

Central Station was planned to provide an underground pedestrian link to the Blue Line at Aquarium station—currently the only rapid transit line without direct connections to North or South Stations—thereby reducing transfers for commuter rail riders heading downtown and alleviating congestion within transit hubs. Similar to Philadelphia’s SEPTA Center City Commuter Connection, certain Boston trains could be operated through both sides of the system while others would terminate at existing surface tracks outside of tunnels, allowing operational flexibility.

A 2003 environmental impact statement estimated that about one-third of southbound Amtrak trains would be routed through the tunnel system, stopping solely at South Station and a new northern stop at Anderson Regional Transportation Center in Woburn. The Downeaster service from Maine and New Hampshire would stop exclusively at North Station with connections available at Anderson RTC rather than continuing into Boston proper. This approach preserved some surface operations and retained all existing facilities.

Because steep grades combined with frequent stops render diesel locomotives unsuitable for tunnel operation, electrification of several commuter lines was deemed essential for efficient use of these tunnels.

Route map

The illustration below depicts one of the most comprehensive plans proposed so far. The 2018 feasibility study options do not incorporate a connection to the Old Colony and Greenbush lines. Among the alternatives, only the four-track configuration includes a link to the Fairmont Line along with a Central station. In two of the scenarios, the surface-level North Station would be removed, and it might also be eliminated in other options.

Route map of the North–South Rail Link (Central Artery Four-track Alignment)
Template:North–South Rail Link

Status

Massachusetts ceased its sponsorship in May 2006, citing the project's substantial capital expense, estimated at several billion dollars. The absence of local matching funds rendered it ineligible for federal grants, leading to its exclusion from state and Boston MPO capital planning documents. Nonetheless, the Boston Region MPO’s April 2007 plan advocated for safeguarding the right-of-way for possible future development.

In December 2007, the Federal Railroad Administration indicated willingness to provide funding if Massachusetts resumed sponsorship. By August 2009, the project was included in the New England transportation plan to compete for a portion of $8 billion designated for high-speed rail under the American Recovery and Reinvestment Act.

Former Governor Michael Dukakis has persistently championed the rail link, urging state officials to prioritize it over expanding South Station. In January 2014, he expressed a preference for naming the project after himself rather than South Station. Later, in August 2015, Dukakis joined former Governor William F. Weld in authoring an op-ed describing the link as "one of the most important and cost-effective investments we can make." Their advocacy contributed to MassDOT allocating $2 million for a study in February 2016.

In June 2018, MassDOT issued a North South Rail Link Feasibility Reassessment that evaluated multiple tunnel options. The state had solicited bids for this $2 million study in March 2017; however, no funding source was identified for construction. On September 6, 2018, MassDOT released a draft feasibility report and invited public feedback by October 19.

Alternatives

By 2018, both MBTA and Amtrak utilized the Grand Junction Line for non-revenue transfers between their systems. This connection branches off from the Framingham/Worcester Line near Boston University and close to the Mass Turnpike exits at Allston and Brighton, crossing over the Charles River into Cambridge. The route continues through East Cambridge into Somerville, where it links with commuter rail lines from North Station near the McGrath-O'Brien Highway.

East of Massachusetts Avenue, this segment is single-tracked and operates slowly due to numerous level crossings. At several intersections—such as Massachusetts Avenue, streets near Kendall Square, Cambridge Street, and Gore Street—trains must nearly come to a halt before proceeding at speeds up to . The corridor is also envisioned as serving a potential West Station within plans for redeveloping Beacon Park Yard.

The Grand Junction corridor has been explored as a possible route for the Urban Ring light rail or bus rapid transit system or alternatively converted into a pedestrian path. However, only trains on the Worcester Line would have direct access; those originating from South Station lines would be required to detour west of Back Bay and Lansdowne stations and reverse direction to connect.

External links

North South Rail Link – website dedicated to advocacy