The project will restore passenger rail service between Boston and the cities of Taunton, Fall River, and New Bedford, via the towns of Berkley and Freetown, on the south coast of Massachusetts.

[4] Initial service will have 16 weekday and 13 weekend round trips between Boston and East Taunton, split between Fall River and New Bedford.

The New York, New Haven and Hartford Railroad leased the entire Old Colony system beginning in 1893, and ran commuter and intercity service to Fall River and New Bedford.

[9] In March 1991, newly elected governor William Weld asked the state legislature to authorize the sale of bonds to finance further studies.

[11] The Old Colony mainline was rebuilt with restricted single-track sections through parts of Dorchester and Quincy, limiting the capacity required for reaching the South Coast via Middleborough — such that service could be operated to one of Fall River and New Bedford, but not both.

[12] In August 1996, Weld signed a bill giving $136 million to commuter rail expansion, while the state legislature directed the MBTA to further study alternatives.

[2] The FEIS was released in April 2002 and approved in August; however, in July 2002 the MBTA revised the project cost to $600 million with an opening date of 2007.

[2] In October 2004, the Southeastern Regional Planning and Economic Development District restarted the Growth Task Force, even while the MBTA was conducting its review of the project.

[16] A Strategic Environmental Permitting Plan was released in August 2007, followed by a Phase 1 Alternatives Analysis Report in April 2008 which narrowed 65 options (including unlikely modes like heavy rail metro and monorail) to five plausible alternatives including Attleboro, Stoughton, and Middleboro routes plus express bus service or a mixture of Attleboro and Middleboro service.

"[22] However, the state continued to publish studies, releasing the South Coast Rail Economic Development and Land Use Corridor Plan in June 2009 and the Phase 2 Alternatives Analysis Report (which indicated electric or diesel service through Stoughton as the best choice) in September 2009.

Other parts of the agreement included plans for double-stack freights west of Worcester and the abandonment of Beacon Park Yard.

[26] On June 11, 2010, the state and CSX completed the first phase of the agreement, including the transfer of the South Coast Rail lines to MassDOT.

[28] Concurring with previous documents it recommended that South Coast Rail be routed through Stoughton, citing in particular the need to add a billion-dollar fourth track from Back Bay to Forest Hills to accommodate service through Attleboro.

However, the DEIS differed from the previous reports by strongly recommending that service be electric, stating that the higher ridership (9,580 projected daily riders versus 8,140), decreased travel time due to the higher acceleration of electric locomotives and their 100 mph top speed versus 79 mph for diesels, and reduced pollution outweighed the increased cost of electrification.

[30] As of February 13, 2025[update] the project website states that Phase 2, "presents more challenges related to wetland impacts, complex engineering, electrification, and cost.

[34] The spending bill, which also included $1.3 billion for the Green Line Extension and $300 million for South Station expansion, was then sent to the Massachusetts House and Senate for debate.

[36] On April 22, 2019, Massachusetts Department of Transportation Secretary Stephanie Pollack announced that funding and Army Corps of Engineers permits for the Phase 1 plan were in place and that the project would proceed "full speed ahead," with a late-2023 target date.

[37] In July 2019, the Baker-Polito Administration filled an $18 billion transportation bond bill that included $825 million for Phase 1 South Coast Rail.

[38] The total cost of Phase 1 is $1.047 billion and will be paid entirely by the Commonwealth of Massachusetts through bonds under the Rail Enhancement Program.

In February 2010, MassDOT received a $20 million TIGER grant to replace three bridges in New Bedford built around 1907, for immediate freight use and future South Coast Rail service.

[47] In mid-November 2013, MassDOT replaced 42,000 ties along 33 miles (53 km) of the Fall River and New Bedford branches, funded as a freight improvement project that also serves as a prerequisite for South Coast Rail.

[53] While MassDOT managed the early action culverts and bridges contracts, oversight of the program was transferred to the MBTA in preparation for the start of Phase 1 construction in 2019.

[57] The $403.5 million contract was awarded to SCR Constructors (a joint venture of The Middlesex Corporation and Tutor Perini) on August 24, 2020; construction began later in 2020 and was estimated to take 37 months.

[57][63] Replacement of a bridge carrying Route 24 over the New Bedford Secondary in East Taunton was originally planned to be part of South Coast Rail as Contract #5.

[67] In 2022, granite blocks from culverts and bridge abutments replaced during the project were dumped into Nantucket Sound off Yarmouth and Harwich to create artificial reefs.

[69] Substantial completion of the Fall River Secondary work was announced in December 2022, with revenue service still planned for late 2023.

[78] Dispatching for the lines shifted from Massachusetts Coastal Railroad to Keolis (the MBTA Commuter Rail operator) in August 2024.

[80] On February 7, 2025, the MBTA announced that Phase 1 service would begin on March 24, 2025, pending final approval by the Federal Railroad Administration.

[85] Due to the sensitive environmental area, an 8,500-foot (2,600 m) elevated trestle is proposed at a cost of $50 million to allow animals to pass under the tracks and limit the disturbance to the existing ground.

[86] The trestle would use concrete box girders on piles spaced at 50 feet (15 m), with a maintenance siding in the middle for rescue operations on disabled trains.