MBTA North South commuter-rail project could cost up to $22 billion

The Massachusetts Bay Transportation Authority's (MBTA) proposed North South commuter-rail project could cost $12.3 billion to $21.5 billion, according to an ongoing feasibility study.

The project calls for building 2.8-mile-long tunnels to connect Boston's North and South stations. The cost estimates cover tunnel construction, new or additional locomotives or coaches, improvements to support higher service levels and risk contingencies, MBTA officials said in a press release.

The study is examining two- and four-track tunnel options. The North South Rail Link could increase capacity by 25 percent, according to the agency.

In July 2017, the Massachusetts Department of Transportation tapped Arup to conduct the feasibility reassessment. While the study's draft is pending, the MBTA's Fiscal and Management Control Board earlier this week received a preview.

The final report is expected to be released in early fall.