The North South Rail Link (NSRL) is a proposed underground tunnel connecting Boston’s North and South Stations, eliminating the one-mile gap that divides the regional rail network and prevents through running across Greater Boston and the Northeast Corridor. This study evaluates the economic case for the NSRL by estimating costs and benefits incremental to full Regional Rail implementation and by examining alternative approaches to implementation. Projected incremental benefits substantially exceed incremental costs: under the Maximum Build scenario (two tunnels, four tracks), the NSRL generates 37.6 billion dollars in benefits against 8.0 billion dollars in incremental costs. By replacing terminal operations with through running, the project could reduce average passenger wait times by 71 percent, more than double rail ridership, and substantially expand regional access to employment. Improved connectivity could also encourage residential development around existing stations and broaden the geographic distribution of housing demand, although these effects depend on local land-use policies. Finally, the study introduces a potential phased implementation approach in which the tunnel is built to full Regional Rail specifications and begins with a frequent, dedicated shuttle between the two stations. This could generate benefits immediately upon completion and accommodate additional lines as the system is modernized.
