The nearly 100-year-old Dorchester Avenue Bridge that links Dorchester and South Boston will be replaced starting this weekend, causing closures on the commuter rail and Red Line, MBTA officials said.
Commuter rail service on the Kingston, Middleborough, and Greenbush lines will be suspended between South Station and Braintree station from 7:30 p.m. Friday through Sunday this weekend and the following two.
Free shuttle buses will replace trains, the MBTA said.
“This service change is in place because these commuter rail lines run adjacent to the Red Line where Dorchester Avenue Bridge Replacement Project work is taking place,” the MBTA said.
Red Line service will also be suspended on March 30 and March 31 and the following weekend between Broadway and Ashmont stations on the Ashmont branch, and between Broadway and North Quincy stations on the Braintree branch.
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Free shuttle buses will stop at all affected Red Line routes.
“There will be free fares at Broadway and North Quincy stations with the fare gates open,” the MBTA said. “Riders boarding Mattapan Line trolleys at Ashmont also do not have to pay a fare.”
During these upcoming weekends, work crews will demolish the existing bridge superstructures and dismantle the bridge spans, T officials said.
The bridge was originally built in 1925 and rehabilitated 50 years later. Officials said the $34.5 million replacement project will protect the bridge’s structural integrity and ensure “reliable service.”
“When complete, this project will result in safer, more reliable Red Line service,” the MBTA said. “The MBTA will also perform upgrade work to the Red Line signal system.”
The Dorchester Reporter previously reported on the bridge replacement.
According to an online overview of the project, the “superstructure replacement” phase of the project is slated to run through the summer, with the bridge reopening to traffic in the fall. The project is scheduled for completion in “late 2024,” according to the overview.
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Construction began in the summer of 2022, and the bridge reopened for pedestrians in July.
Travis Andersen can be reached at travis.andersen@globe.com.