With holiday exceptions, there will be no weekend commuter rail service between the Fitchburg and South Acton stations starting on Saturday and continuing through mid-November while improvements are made to the tracks. Trains between South Acton and North Station will operate on the normal weekend schedule until Aug. 3, when the service suspension will be extended from South Acton to include Kendal Green Station in Weston; weekend trains serving North Station will begin and end at Brandeis/Roberts Station until Nov. 17, according to an announcement by the MBTA. Substitute busing will not be provided between the closed stations, and weekday service will not be affected. Weekend train service will be provided for the Memorial Day, Fourth of July, and Labor Day weekend holidays, however. The Massachusetts Bay Transportation Authority and Montachusett Regional Transit Authority are making extensive improvements to modernize the 50-mile commuter rail line between Fitchburg and Boston. The $159 million project includes installation of new switches and signals, renovation of two stations, and reconstruction of existing track on the state’s oldest commuter rail line, which serves 17 communities at 18 stations. For more information, visit www.mbta.com and click on service alerts for the Fitchburg commuter line.