An MBTA commuter rail train pulls out of the station in Chelsea. Photo by Piper McCorkle | CC BY-SA 2.0

Passenger service on a commuter rail expansion to southern Massachusetts is not expected to begin until next summer, about half a year later than prior forecasts, MBTA officials said Thursday.

During a wide-ranging presentation about the status of the highly anticipated South Coast Rail project, MBTA Chief Operating Officer Ryan Coholan told the agency’s board that “revenue service is expected to begin [in] summer of 2024.” A range of safety and certification steps need to be “satisfactorily and successfully completed” first, he said.

The reflects a delay of several months from what MBTA officials previously expected. At a ribbon-cutting for the expansion in December, former MBTA General Manager Steve Poftak said riders should be able to begin riding South Coast Rail by the end of 2023. The official T website on Thursday said “construction is expected to be completed in late 2023.”

An MBTA official said work will focus on automatic and positive train control safety systems, employee qualifications and safety education about the rail right of way during the additional time created by the delay.

“I commend the South Coast Rail team for their resolute commitment to this project, including working through a pandemic and managing supply chain issues, to bring us the point where we are about to begin the testing of the new railroad’s critical safety components, including Automatic Train Control for maintaining proper speeds and Positive Train Control for preventing collisions,” MBTA General Manager Phil Eng said in a statement. “This testing will continue as we train, qualify and certify the locomotive engineers who will help us provide this eagerly anticipated service to the people of Southeastern Massachusetts.”

The $1.1 billion project’s first phase will bring about 36 miles of track online for commuter rail service linking Boston to New Bedford, Fall River and several other communities in the region. A version of the expansion has been under consideration for decades.

Coholan said the last comparable project was the launch of the Greenbush Line in 2007, which he noted is “about 20 miles shorter.” He rattled off a long list of South Coast Rail features, including stations at Middleborough, East Taunton, New Bedford Church Street, Freetown and Fall River, new tracks, and dozens of bridges, culverts and grade crossings.

“It’s like Christmas every day for someone who operates a railroad,” Coholan said.