A Green Line trolley motors through a ceremonial ribbon pulled across the track at the brand-new Lechmere Station on Monday, March 21, 2022. The event celebrated the start of service on the Green Line Extension's Union Square branch. Photo by Chris Lisinski | State House News Service

It turns out it won’t just be the entire MBTA Orange Line shutting down between mid-August and mid-September.

The MBTA announced it will halt its Green Line service north of downtown Boston from Aug. 22 through Sept. 18 to prepare for the planned opening of the Green Line’s Medford branch.

That branch will now open in late November 2022 after delivery was promised for this summer.

Instead of continuing on to the commuter rail terminal at Boston’s North Station, East Cambridge and Somerville’s Union Station, the Green Line will terminate at the Government Center station in front of Boston City Hall. Orange Line and Green Line shuttle buses will both end their routes from points north of downtown there, as well.

The T says the month-long shutdown, which will eliminate all subway service for a huge swath of Greater Boston north of downtown Boston along with the simultaneous Orange Line shutdown, is necessary to let construction crews “safely and quickly complete work deemed critical to the opening of the new Medford Branch.” The shutdown also means riders using the Haverhill commuter rail line to replace their Orange Line trips won’t be able to transfer to subway trains at North Station, along with the thousands who use commuter rail trains to travel in and out of the city daily to points north and west of Boston.

During the shutdown, the T says it will complete four projects:

• “Adjustments” to the overhead wire power system on the elevated tracks between North Station and Union Square that will eliminate a temporary 10 mph speed restriction on the line, allowing trains to operate at the system’s designed speed of 25 mph on a permanent basis. The T said the higher speed is needed so trains can “maintain proper schedule intervals as five new Medford Branch stations are added to the system.”
• Completing testing of track switches, power lines, signal equipment and digital communications between the Green Line’s Union Square Branch, the soon-to-be-operational Medford Branch and the control center that oversees all MBTA subway trains and trolleys.
• The installation of more sound wall panels along the Union Square Branch and “non-critical”” work items along the Medford Branch.
• “Additional last work and various outstanding construction items” along the Union Square and Medford Branches.

The work will also allow HYM Investments to conduct more demolition work on the unsteady Government Center Garage that hangs over the Haymarket station on the T’s Orange and Green Lines, the T said. The garage’s foundations were found to be severely deteriorated earlier this summer, prompting an emergency subway shutdown until the foundations could be shored up, and a portion of the garage collapsed while being demolished in March, killing a construction worker.