A draft study by the Massachusetts Bay Transportation Authority (MBTA) has found connecting its north and south commuter rail networks via a rail tunnel would add up to 25 percent capacity, but cost between $12.3 and $21.5 billion.
The North South Rail Link (NSRL) was first analyzed in the late 1990s/early 2000s and was slated for reassessment in 2016. A preview of the NSRL Feasibility Reassessment has been released pending finalization of the draft report.
According to MBTA, the feasibility of the NSRL from the perspective of infrastructure was found to depend largely on tunnel and station depths. Station depths of 115 and 195 feet—deeper than the Red Line’s Porter Square Station, the MBTA’s current deepest station—would be required.
Additionally, construction of the Back Bay portal would prevent any trains from accessing South Station from the west and most from accessing it from the south (other than the Fairmount and Old Colony Lines) during the roughly two-year construction phase of the portal. This means the termination of Worcester Line service west of Back Bay and the potential rerouting of Amtrak Northeast Corridor, Franklin Line and Providence Line service via the Fairmount Line for two years.
All NSRL station platforms would also be underground and would maintain current connections into today’s South Station headhouse (Red and Silver Lines) and North Station subway (Green and Orange Lines). All northside service was also assumed to run through the NSRL tunnel, meaning that surface-level tracks and platforms would not be required for revenue service.
Ridership projections ranged from 195,000 to 250,000 and the estimated ridership of the “No Build” option was 150,000. The draft study shows the NSRL would increase capacity by 25 percent in terms of the number of commuter rail seats arriving in Downtown Boston during the peak period.
Total costs, including all costs associated with the tunnel construction, new or additional locomotives or coaches, upstream improvements needed to support increased service levels and risk contingencies, range from $12.3 billion to $14.4 billion for the two-track alignment options and $21.5 billion for the four-track alignment.
MBTA will present the NSRL reassessment findings at a public meeting held on June 21. The draft NSRL Feasibility Reassessment will be released in early July 2018 followed by a public comment period and a final NSRL Feasibility Reassessment Report slated for finalization in early fall.