Significant portions of the subway system will be shut down on weekends and evenings and replaced with shuttle buses starting this weekend and extending through the fall. Here's what's happening:

Orange Line

Wellington to Oak Grove: Shuttle service Mondays through Thursdays after 8:15 pm until 1:25 am, August through December 2019.

Ruggles to Forest Hills: Shuttle service weekends, starting Friday at 8:45 pm and running all day Saturday and Sunday during August and September.

Tufts Medical Center to Sullivan Square: The MBTA has announced plans to shut stations between Tufts and Sullivan on weekends in October and November. More details are expected soon.

Red Line

Broadway to Kendall: A plan to shut stations between Broadway and Kendall, including South Station, on some weekends in December and November, has been floated by T officials. More details are expected soon.

Green Line

D Line, Newton Highlands to Kenmore: Shuttle buses replace trolleys after 8:30 pm until 12:49 am, Monday through Friday, August through Dec. 20, 2019.

B line, Blandford to Washington: Shuttle buses replace trolleys the weekend of Aug. 17. The disruption begins Saturday morning.

Commuter Rail

Fitchburg Line, Porter Square to North Station: Service will not be running in both directions weekends from August through Sept. 29. Free subway connection will be provided at Porter Square and North Station.

Lowell Line, Anderson RTC to North Station: Weekend service will be replaced with shuttle buses from Oct. 25. Normal service will operate the weekend of Aug. 17-18, August 30-31, and Sept. 1.

Needham Line: There will be no Needham line service on the weekends August through Oct. 12. No shuttle buses are being scheduled; MBTA suggests using alternative bus and subway routes.

Franklin Line: Shuttle buses replace trains on weekends through Nov. 24 between Forge Park/495 and Readville; no service at Back Bay, Ruggles, Endicott, Islington, or Norwood Depot.

Service changes on the MBTA happen frequently: check before you go.