The long-stalled plan to bring rail service to the South Coast will cost nearly $1.2 billion more than projected and take until at least 2030 to complete, according to state officials, who warn hard decisions lay ahead on how to make good on a decades-long promise to connect the region to South Station.

The project, known as South Coast Rail and initiated in 1994, is now projected to cost $3.4 billion, a more than 52 percent jump from the $2.23 billion price tag state officials unveiled in 2012.

At the time, state officials under the Patrick administration estimated it would take 10 years to finish the project, or by 2022. Now under the Baker administration, MassDOT — which began assigning small contracts in 2014 — says it will take 16 years, pushing a projected completion date to 2030.

Transportation Secretary Stephanie Pollack was expected to brief lawmakers from the region on the new details this morning. In a meeting with reporters, she stressed that Gov. Charlie Baker and her remain “100 percent committed to getting trains to the South Coast.”

But she said she has concerns, both with the new cost estimates and the time it would take to complete.

“The question is, what still makes sense?” Pollack said. “One of the concerns I have aside from the cost issues … is simply this issue, that the folks on the South Coast have been promised this service for a long time.”

The project, to which the state has already committed $24 million, would expand rail service through 10 communities from Stoughton to New Bedford and Fall River, serving an estimated 4,570 riders a day.

But the plan comes with a host of complications, from navigating a web of environmental permits to developing the MBTA’s first “electrified” train system. That includes upgrading 75 miles of track, purchasing 10 new locomotives and 50 cars, and updating three dozen bridges, according to MBTA general manager Frank DePaola.

DePaola said in 2012, officials estimated that completing the permitting process would take three years. Now, it could take up to 6 1/2 years. For every month that the project is stalled, $4.1 million is added to the bottom line, he warned.

The new price estimates follows a similar report on the T’s beleaguered Green Line extension project, which is proceeding despite its ballooning costs.

The potential for a drawn-out South Coast project has prompted state officials to look at alternatives: Expanding service not from Stoughton but from Middleboro, and adding four more trains during peak service instead of creating the more complicated network called for under the original plan.

The option was scrapped during initial planning, Pollack said, because it would route riders through the system’s Old Colony Line, which wouldn’t be able to handle the additional volume.

But DePaola said officials reconsidered when an outside firm came to MassDOT with an “unsolicited” proposal roughly eight months ago to reshape a portion of I-93 in the Savin Hill section of Boston by expanding the highway by two lanes and pushing the MBTA and commuter rail tracks underground. The highway project would create a second commuter rail track underground, creating the capacity to add more riders through the Old Colony Line and thus from Middleboro and beyond.

DePaola said he didn’t have a cost estimate, and officials stressed that it isn’t a plan they’re pursuing — only one they’re looking for feedback on if the MBTA’s fiscal management and control board, lawmakers and others deem the original South Coast Rail plan to costly and time-consuming.

“We’ll put this on the table and if there’s an interest, we can do additional work,” Pollack said. “Today we don’t have an answer of what it will cost (or) how long it will take to build.”