Dive Brief:

• A proposed three-mile underground rail line joining Boston's busy North Station and South Station would cost between $4 billion and $6 billion, according to a Harvard Kennedy School study.

• The study revealed that the rail could be built for markedly less than was originally thought, making the project more attractive, The Lowell Sun reported. Proponents maintain that the North-South Rail Link could provide better access to the city's business districts and help reduce train traffic congestion.

• The Massachusetts Department of Transportation commissioned a separate, $1.5 million study from Arup USA, which is scheduled for completion in 2018. The results, which will include projected costs and benefits, will help MassDOT officials decide whether the rail line is viable.

Dive Insight:

Massachusetts transportation officials are hedging their bets with multiple studies given the department's rocky history with major rail projects — namely the Boston Green Line extension. That project made headlines when the Massachusetts Bay Transportation Authority (MBTA) fired all the primary contractors in December 2015 after cost overruns hit $1 billion. After revising the project, bringing costs down and showing the Federal Transit Administration that it was still viable, the MBTA is on track to restart construction under a design-build model.

Earlier this year, Sen. Elizabeth Warren (D-MA) expressed her support for another potential major rail project — a high-speed rail line between Springfield, MA, and Boston. Warren said the project could jive with President Donald Trump's expected $1 trillion infrastructure plan, prompting state lawmakers to advocate for its inclusion among the administration's designated projects.

Without state support, a high-speed line is a virtual nonstarter. Even if proponents could manage to secure federal funding, Massachusetts would most likely have to come up with matching funds, much like Minnesota's $1.9 billon Southwest light-rail line.

The Massachusetts high-speed rail project could likely run up against resistance from landowners opposing eminent domain. Texas Central Partners — developers of a privately-financed, high-speed rail system proposed between Houston and Dallas — have encountered resistance from residents in the line's path. Those residents say they don't want to sell their land to Texas Central, disputing the developer's right to acquire the land through eminent domain.