The North–South Rail Link (NSRL) is a proposed rail tunnel, or pair of tunnels, that would connect North Station and South Station in downtown Boston, Massachusetts, linking rail networks that serve the city's northern suburbs, New Hampshire, and Maine with the rest of the country. The project would build new underground stations near the existing stations, connect them with about of tunnels, and add other tunnels to link up with existing surface tracks.
The NSRL would connect Amtrak and MBTA Commuter Rail lines that terminate either at North or South Station. For MBTA, it would link northern lines to South Station, Back Bay Station, and lines beyond Back Bay, including the Framingham/Worcester Line and the Northeast Corridor; one option under consideration would also link to commuter lines to the south. The project would also link Amtrak's various trains into and out of the city; for example, the Downeaster line from Maine currently has no direct connection with Northeast Corridor trains to New York City and beyond.
In 2017, a Harvard Kennedy School study estimated the cost of the NSRL at $4 to $6 billion (in 2025 dollars), based on Federal Transit Administration data and an analysis of comparable tunnel projects around the world. A 2018 MassDOT study looked at four options with estimated costs ranging from $12 billion to $22 billion (in 2028 dollars).
As of , the North-South Rail Link has not been pursued and is not in active development, though advocates call for updated studies.
Historical connections
From 1872 to 1969, the freight-only Union Freight Railroad provided a direct, street running connection between most of the south-side and north-side railroads, and served local customers and wharves in between.
From 1901 to 1938, the Atlantic Avenue Elevated provided direct passenger service past North and South Stations. The elevated trackage was not connected to any of the conventional railroad tracks.
The Grand Junction Railroad, specifically its western segment, remains as the only rail connection between the north and south railroads in the Boston area.
Present connections
Public transit connects North Station to South Station only indirectly, through two of the MBTA Subway system's quartet of hub stations. A trip between the two commuter rail stations requires taking two subway lines – either the Green Line and the Red Line through their shared Park Street station, or the Orange Line and the Red Line via their shared Downtown Crossing station. It can also be done by walking between the two stations, which takes between 20 and 30 minutes. Amtrak recommends that passengers with young children or much luggage take a taxi or rideshare between the stations.
It is possible to traverse the gap directly via the Orange Line from Back Bay Station to North Station, but it requires seven stops and only four of the southern lines pass through Back Bay. The Orange Line also provides a connection for Amtrak passengers who want to transfer between the Northeast Corridor and the Downeaster. However, North Station passengers add to Orange Line congestion. Similarly, it is possible to connect between South Station and the Fitchburg Line via the Red Line at Porter station. Passengers on the Newburyport/Rockport Line can also take the Silver Line from Chelsea (Bellingham Square). MBTA bus route connects the two stations, albeit only at weekday peak hours.
The North–South Rail Link is proposed to fill all these gaps in service, with direct connections requiring no transfers.
2018 NSRL feasibility study
In June 2018, MassDOT released a North South Rail Link Feasibility Reassessment presentation that described several tunnel alternatives. The state began soliciting bids for a $2 million feasibility study on March 1, 2017. This study had been pushed for by the North-South Rail Link Working Group. The working group, NSRL supporters, includes Senator Ed Markey, Representatives Niki Tsongas and Katherine Clark, with Representative Seth Moulton leading the effort. It also includes more than half of Massachusetts mayors.
Options The 2018 MassDOT feasibility study analyzed four options. The costs, presented in 2028 dollars, include purchasing additional rolling stock, other required infrastructure improvements, and a 3.5% annual inflation. Presenters noted that a planned expansion of South Station would cost an estimated $4.7 billion, not including the purchase of rolling stock, electrifying the system, and renovating Tower 1.
Two options would run under the Central Artery (I-93), one option with two tracks and the other, more expensive, with four. The other two options, each with two tracks, would tunnel under downtown Boston several blocks west of the Artery. All the proposals connect the northern commuter rail lines with South Station and then to Back Bay and lines to the west. Only the four-track option would connect North Station with the Fairmount Line south of South Station. Under all the proposals, lines using the Old Colony main line (the Greenbush, Kingston, and Fall River/New Bedford lines) would continue to terminate at the South Station surface platforms. The existing North Station and its surface platforms could be eliminated under all four options, making the area available for redevelopment.
Central Artery four-track The most ambitious option is the only one that includes a new Central station (or Union Station) near its midpoint, and the only one with a rail tunnel connection to the Fairmount Line. North Station would be underground near the present station. The line would be constructed using two TBM tunnels, deep, along with cut-and-cover in Fort Point Channel. Underground South Station would be built in Fort Point Channel, east of the surface station. Central station would connect to the Blue Line at Aquarium station. The Blue Line is currently the only MBTA rapid transit line with no direct connection to the commuter rail network. Estimated cost: $21.491 billion.
Central Artery two-track Same route as Central Artery four-track but has no Central station. Constructed using one TBM tunnel, deep, with cut-and-cover used in Fort Point Channel. Underground South Station would be built in Fort Point Channel, east of surface station. Estimated cost: $12.317 billion.
South/Congress alignment North Station would be entirely underground and moved several blocks south, to between State and Haymarket Streets; no Central station. Stacked tracks and platforms are incorporated within a single TBM bored tunnel, deep. Underground South Station would be north-west of surface station. Estimated cost: $13.181 billion.
Pearl/Congress alignment North Station would be entirely underground and moved several blocks south, to between State and Haymarket Streets; no Central station. Tracks would be in two TBM bored tunnels, deep. Underground South Station would be north of surface station. Estimated cost: $14.388 billion.
Electrification The tunnels would not be able to handle diesel locomotives and therefore would require the use of dual-mode locomotives or the electrification of several MBTA commuter rail lines. Full electrification of additional rail lines, proposed in earlier studies, could help Massachusetts and the MBTA reach their greenhouse-gas reduction goals, make service more reliable, allow trains to accelerate more quickly, and reduce travel times, but it is expensive and only limited electrification is included in the 2018 proposals. Part of the Fairmount Line would be electrified to allow Amtrak and MBTA Northeast Corridor trains currently routed through Back Bay to reach South Station during construction of the Back Bay portal. The electrified service region would also incorporate the proposed South Coast Rail project's Phase II, which includes electrification to Fall River and New Bedford.
Benefits
The 2018 feasibility study modeled ridership in 2040 based on various scenarios. In regular service, the two-track options would increase all day boardings to 195,000 compared with 150,000 in the no-build scenario. Assuming an upgrade to all-day peak service, the two-track options would increase all day boardings to 225,000 compared with 195,000 with the South Station expansion. Overall, NSRL would increase commuter rail capacity, in terms of seats to downtown, by 25%.
The feasibility study presentation also projected the distribution of destinations for commuters coming from the north in the morning.
+NSRL Projected Morning Trips From The North in 2040, Two-Track Destination Passengers Percent 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 issues
The 2018 feasibility study identified several potential problems and risks with the NSRL project. During construction of the Back Bay tunnel portal, required under all options, the MBTA Worcester Line and Amtrak Lake Shore Limited service would have to terminate west of Back Bay station or possibly be rerouted via the Grand Junction Line into North Station. Also some or all Amtrak, Providence, Stoughton, and Franklin Line service would be rerouted via the Fairmount Line into South Station.
The proposal makes aggressive assumptions about improved passenger loading and unloading times and on how many trains can operate per hour in the tunnels. The proposed train frequency, 17 per hour per direction in the two-track options, is higher than the current Red Line train frequency, and exceeds what has been achieved to date on other systems that use the new positive train control systems required for heavy rail. To maintain the 17 trains/hour frequency, trains would have to arrive to enter the tunnel precisely as scheduled. However, new systems like Thameslink in London, UK, have shown that up to 24 trains per hour are possible on heavy rail.
With the NSRL, the MBTA commuter rail system would be highly dependent on the tunnel routes. Any disruption to those routes would affect the entire system.While the NSRL design as proposed exceeds National Fire Protection Association NFPA 130 life safety requirements, evacuation of the deep tunnels and stations in case of fire could still be difficult. The deep stations would also cost passengers additional time entering and leaving. Currently Porter Square station, at 105 ft, is the deepest in the MBTA system.
Early proposals There have been several proposals to link South Station and North Station by rail. In 1987, Congress included funding for the link in a highway and transit bill, but it was dropped after Ronald Reagan vetoed the bill.
A North-South Rail Link was included in the original Big Dig design, but was dropped by the Dukakis Administration. An earlier leading proposal, called the "Dorchester Avenue Alignment", is similar to the four-track Central Artery alignment in the 2018 study. It would dig two deep-bore tunnels beneath Boston, extending beyond the present rail yards north and south of the city. The tunnels would pass about beneath the I-90 extension, and would reach their maximum depth of at a possible Central Station and at North Station. Carrying a total of up to four tracks, the tunnels would have steep inclines. Trains entering or exiting the tunnels would climb or descend 3% grades, each nearly long.MBTA, et al., North South Rail Link Project, Major Investment Study, vol. I, figure 2.5–7 (June 2003).