Photo courtesy of the MBTA

The MBTA will postpone the opening of a Green Line Extension stop in Somerville by three months, and the already-delayed May 2022 goal for the remainder of the megaproject may also run into issues, officials announced Thursday.

Calling it “disappointing news,” MBTA General Manager Steve Poftak said the transit agency now expects to reopen the Green Line’s Lechmere Station and open a brand-new stop in Somerville’s Union Square in March rather than in December.

The $2.3 billion rail expansion is approaching completion after a rocky, decades-long history featuring a lawsuit, canceled contracts and several delays.

And while the project remains on target for its current budget, T officials continue to push off the final opening amid construction hiccups, some inflicted by the COVID-19 pandemic.

Poftak said “a variety of challenges” contributed to the latest delay on the Union Square-bound chunk of the project, particularly during work on a facility that will help provide power to the system.

That facility, known as a traction power substation, converts energy to be used by the trolleys that run on the Green Line. During construction, Poftak said the building’s tight quarters meant “only so many people” could fit inside and do the technical work needed.

Workers need to build two more similar substations for the second branch, Poftak said, though he noted that they have “a little bit longer window” of time for those facilities. The T hopes to use the stumbling blocks on the Union Square branch as a lesson for the rest of the project.

“It is one of the challenges we are facing and it is one of the areas that we’re concentrating on as one of the critical path items,” Poftak said. “If we’re not more productive and more efficient in building out these next two traction power substations, it is going to impact the schedule.”

Construction on the 4.7-mile extension began in 2018.

In June, MBTA officials pushed the goal for the Union Square target from October — itself an earlier deadline than originally set — to December. They also announced that the second, larger Green Line Extension branch adding six stops from East Cambridge to Medford would be postponed from an end-of-year opening to a May 2022 target.

At the time, officials attributed the delay to supply chain problems exacerbated by the pandemic.

Poftak said Thursday that the T is still working to determine the schedule for the rail expansion’s second branch, leaving on the table the possibility that the MBTA could postpone the remainder of the project a second time.

“I do have a real high level of confidence that this will be the last delay, sort of leaving open that we are still working on branch two,” Poftak said. “It was my hope that the announcement in June was our final announcement related to schedule. Obviously, that’s not the case.”

Asked if the May 2022 goal for the remaining six stops are in question, Poftak replied, “I have not abandoned all hope on that.”

“I do want to make sure that I have a level of confidence in that delivery date before I change it, so that is something we’re going to come back to you and talk about once we have a higher level of confidence,” he said.

Unlike the June postponement, the latest delay will not require any changes to the MBTA’s agreement with contractors, Poftak said.

Somerville Mayor Joe Curtatone, long a vocal supporter of the project, told the News Service that he is “frustrated” it will take another three months to open the first expansion stop in his city but that he understands “these things happen” in complex projects.

“At the end of the day, decades of advocacy and broken promises — that’s long gone,” Curtatone said. “We’re just about there. We’re turning the corner and we’re just a few months away from seeing full operation.”

New sections of the Green Line will not launch with anti-collision technology that the MBTA expects to implement by 2024. That feature, which had been recommended as far back as 2008, was thrust into the spotlight this summer when a speeding Green Line trolley on the B Branch struck another train from behind.

“I do believe that we will accelerate that project. The extent of the acceleration I think we are still in the process of determining,” Poftak said Thursday.

Construction on the project remains on budget despite the delays, and its financial footing could soon result in millions of dollars flowing to Cambridge and Somerville.

The two cities, which will each be home to new rapid transit stops following the expansion, helped float the project years ago when its fate was less certain. Somerville pledged $50 million and Cambridge pledged $25 million.

MBTA officials informed Cambridge and Somerville in June that they would not need to cut any more checks toward the Green Line Extension, and Poftak on Thursday said he plans to seek approval this fall from the MBTA’s new board to return the tens of millions of dollars the communities paid.

“We’re confident at this point that the project does not need that money,” he said. “We’re appreciative that the communities were willing to step up when this project was very much in doubt, and we think it’s appropriate at this stage of the project to return the money.”

Poftak initially said the two cities paid a combined $30 million so far, but a spokesperson later clarified that Somerville has paid $30 million and Cambridge has paid $15 million.

Poftak plans to bring the refunds forward for a vote before the MBTA Board in November. That panel, which succeeds the Fiscal and Management Control Board that dissolved at the end of June, will host its first meeting in October, when Poftak said members will still be getting up to speed.

While the delay may cause frustration for riders who want to reach Union Square on the Green Line, one transportation advocate said the decision should not raise too many red flags.

“Unfortunately, many transit agencies across the country are dealing with supply chain issues and staffing shortages — which are contributing to delays like this,” said Stacy Thompson, executive director of the LivableStreets Alliance. “I don’t believe this is a cause for concern at this time and look forward to celebrating the opening of the long awaited Green Line extension in March.”

The three-month postponement means that Curtatone, who is not seeking another term after 18 years as mayor, will not be the city’s top elected official when the first Green Line Extension stop opens in Union Square.

“I’d have liked to ride that first train as mayor,” he said. “That’s alright. I’ll ride it as a resident of Somerville.”