Jabarkan Commuter rail dari Massachusetts Bay Transportation Authority

There are several proposed extensions to current commuter rail lines. An extension of the Stoughton Line known as South Coast Rail is proposed to serve Fall River, and New Bedford. Critics argue that building the extension does not make economic sense.

A  extension of the Providence Line past Providence to T. F. Green Airport and Wickford Junction in Rhode Island opened in 2012. The Rhode Island Department of Transportation is also studying the feasibility of serving existing Amtrak stations in Kingston and Westerly as well as constructing new stations in Cranston, East Greenwich, and West Davisville. Federal funding has also been provided for preliminary planning of a new station in Pawtucket.

In September 2009, CSX Transportation and the Commonwealth of Massachusetts finalized a $100 million agreement to purchase CSX's Framingham to Worcester tracks, as well as some other track, to improve service on the Framingham/Worcester Line. A liability issue that had held up the agreement was resolved. There is also a project underway to upgrade the Fitchburg Line to have cab signaling and to construct a second track along a  run near Acton which is shared with freight traffic, so that the Fitchburg to Boston trip will be able to take only about an hour. Completion is expected in December 2015.

The state of New Hampshire created the New Hampshire Rail Transit Authority and allocated money to build platforms at Nashua and Manchester. An article in The Eagle-Tribune claimed that Massachusetts was negotiating to buy property which has the potential to extend the Haverhill Line to Plaistow, New Hampshire.

Massachusetts agreed in 2005 to make improvements on the Fairmount Line part of its legally binding commitment to mitigate increased air pollution from the Big Dig. These improvements, including four new infill stations, were supposed to be complete by December 31, 2011. The total cost of the project was estimated at $79.4 million, and it was expected to divert 220 daily trips from automobiles to transit. , three of the new stations were open; the fourth station has been delayed by community opposition. In 2014, the MBTA announce it would purchase Diesel Multiple Unit (DMU) self-propelled rail cars for the Fairmount Line with eventual expansion to five other lines to be known as the Indigo Line. The planned DMU procurement was canceled in 2015.

No direct rail connection exists between North Station and South Station, effectively splitting the commuter rail network into separate pieces. A North–South Rail Link has been proposed to unite the two halves of the commuter rail system, to allow more convenient and efficient through-routed service. However, because of high cost, Massachusetts withdrew its sponsorship of the proposal in 2006, in communications with the United States Department of Transportation.  Advocacy groups continue to press for the project as a better alternative than expanding South Station, which would also be costly but provide fewer overall improvements in service.