Brookline riders on all four Green Line branches will lose train service into downtown Boston for nine days starting Saturday, Aug. 8, as the MBTA shuts down large sections of the system to upgrade century-old signals in the central subway tunnel.

Service will be suspended through Sunday, Aug. 16. The agency is advising riders to add at least 25 extra minutes to any trip that involves a shuttle bus.

The closure is the broadest Green Line shutdown to hit Brookline this year, affecting the B, C, D and E branches simultaneously. As we reported July 30, the C-branch portion of this work will shut Beacon Street stations. But the full scope covers far more of the town's transit network.

What's closed, branch by branch

B Branch: Service suspended between Government Center and Babcock Street, the branch's Brookline terminus. Free shuttles will run between Babcock Street and Back Bay.

C Branch: Service suspended between Government Center and Cleveland Circle, covering all Brookline Beacon Street stations. Free shuttles will run between Cleveland Circle and Back Bay. Shuttles will not stop at Saint Mary's Street, Kent Street or Brandon Hall.

D Branch: Service suspended between North Station and Kenmore. Free shuttles will run between Kenmore and Back Bay. Trains will continue operating west of Kenmore, so Brookline D-branch riders at stations like Brookline Village, Brookline Hills and Reservoir can still board, but will need to transfer to a shuttle at Kenmore to reach downtown.

E Branch: Service suspended between Heath Street and North Station. No dedicated shuttle buses will run on this branch. Riders should use the fare-free Route 39 bus between Heath Street and Back Bay, then connect to the Orange Line.

Other fare-free options

Route 57 will operate fare-free for the full nine days. The Worcester Line commuter rail will also be fare-free between South Station, Back Bay and Lansdowne, according to MassLive, offering another path downtown for some Brookline commuters.

The signal system is more than 100 years old. MBTA General Manager Phil Eng told WBUR that the work addresses areas the T hasn't yet reached despite prior infrastructure campaigns, adding that without the upgrades, the system would see the return of speed restrictions.

Eng said the T scheduled the work for August because summer ridership is lower and the agency avoided disruptions during the World Cup, tall ships and 250th anniversary celebrations earlier this summer.

"The long-term benefits are going to definitely outweigh the short-term pain," Eng told GBH's Boston Public Radio, as reported by MassLive. "That's why we're trying to announce them as early as possible so people can plan around those days."

Normal service is scheduled to resume Monday, Aug. 17. But riders at Brandon Hall should note that starting that same day, trains in both directions will bypass that station as accessibility work continues. Symphony Station also remains closed for renovation.

Riders can check trip options at mbta.com or through the Transit app. The MBTA has signaled that more Green Line outages are planned later this year.