Connecting the Northeast: A Cost Estimate for the North South Rail Link

This paper presents rough order-of- magnitude estimates for the capital cost of the North South Rail Link (the “Link”), a proposed infrastructure project to connect the commuter rail and Amtrak lines that currently terminate at Boston’s North and South Stations via underground tunnels. The Link’s design and construction cost was estimated using a financial model built from actual line item-costs in the Federal Transportation Administration's database of transportation projects. A regression analysis of comparable completed tunneling projects was performed to validate this estimate. The Link is estimated to cost approximately $5.9 billion in 2025 dollars for the maximum build alternative (two tunnels, four tracks, and three stations). The minimum build alternative (one tunnel, two tracks, and two stations) is estimated to cost approximately $3.8 billion. Both estimates represent a mean of several estimation techniques and are the center of a distribution of possible cost outcomes. The study also identified the areas in which cost overruns have occurred in previous tunnel and rail projects and proposes steps to mitigate against such overruns. The study did not examine the potential benefits of constructing the Link and we recommend further study of both the costs and benefits of this important project.