The Massachusetts Bay Transportation Authority will shutter the Green Line’s D Branch — which runs from Union Square in Somerville to Riverside in Newton — for three separate nine-day closures as part of an infrastructure upgrade project starting this month, the agency said in a statement.
The project will allow the MBTA to replace 6,000 feet of track and make improvements to about a half-dozen station crossings. It also will install equipment for the Green Line Train Protection System, which can automatically stop a train when another vehicle is detected, the statement said.
The majority of the track replacement will take place between Riverside and Eliot stations in Newton. During the full-access closures, the parking lots at Waban and Eliot stations will be closed to the public while they are used for storage of track material and vehicles.
The first Green Line subway branch closure was set to run from Saturday through Oct. 2, according to the MBTA. Subsequent closures are scheduled from Oct. 8 through Oct. 16, and Oct. 22 through Oct. 30.
Alternative service will be available for all D branch riders during the closures, the statement said. Free, accessible shuttle buses will stop at stations between Riverside and Kenmore stations.
The buses will not stop at Beaconsfield station in Brookline due to the narrow roads in the area, the statement said. Riders instead are urged to use Reservoir station, or the C branch’s Dean Road stop to access the Green Line.
The MBTA already has completed projects along the Green Line’s B, C, and E branches this summer, the statement said. Work along those branches included installation of the train protection system, as well as track replacement.
Steve Poftak, the MBTA’s general manager, said the projects allow the T to “accelerate investments and improvements across the system.”
Poftak said he is confident the D branch work will be completed on schedule, and deliver “an increased level of safety and reliability to our riders through track replacement work and the installation of [train protection system] infrastructure.”
The MBTA is facing increased scrutiny after several recent safety issues, including the dragging death of a Red Line passenger in April and a fire aboard an Orange Line train in July.
The Federal Transit Administration, which investigated the MBTA over the safety problems, required the agency to meet dozens of required actions, including performing deferred maintenance on the Orange Line.
That subway service reopened Monday following an unprecedented month-long closure to do the work.
On the Green Line, federal officials recommended more than a decade ago that the MBTA install a system to prevent train collisions, following a crash that killed a Green Line train operator in 2008, and a 2009 crash that left about 50 people injured.
Last year, a Green Line train traveling above the speed limit crashed into another train by Boston University and injured about two dozen people, leading to charges against the train’s operator.
In June, a Green Line train crash at Government Center station sent four people to the hospital.
Globe staff reporter Taylor Dolven contributed to this report.
John Hilliard can be reached at email@example.com.