The brand new branch of the Green Line going from Lechmere to Union Square, which opened to riders just over a year ago, will be shutting down from July 18 to Aug. 28.

But unlike other T closures, this one doesn’t have to do with new infrastructure. The Green Line extension is being taken offline because of a deteriorating bridge over the Green Line's tracks.

MassDOT crews must undertake what is called “critical repair work” on the Squires Bridge by Union Square station. MassDOT spokesperson Jacquelyn Goddard says the bridge repairs will target six steel beams that are necessary for maintaining the integrity of the bridge. The Green Line's overhead power lines, which run underneath the bridge, conflict with repair locations, so electricity on that portion of the Green Line will need to be shut off to allow workers safe access to the deteriorating beams.

Instead of supplying shuttle buses, as the MBTA has done on other diversions, the public transit agency is encouraging riders to instead utilize existing bus routes. Lisa Battiston, a spokesperson for the MBTA, said shuttle bus service is not being considered because riders can walk to the nearby East Somerville stop on the Green Line's Medford Branch or take an existing bus to reach their destination.

Riders can take the 86 or 91 bus to the stop at Washington Street and New Washington Street to access the East Somerville station on the Green Line E branch, from which regular service will operate.

Riders heading toward Union Square can also board the Route 87 bus at Lechmere Station and deboard at Somerville Avene and Stone Avenue.

Jarred Johnson, executive director of TransitMatters, says the T has “got to do a better job” on getting information to riders. He says the T needs to add signage at Union Square informing riders how to navigate the shifted service, adding that scannable codes — like those pasted at Haymarket Station — are not always useful for riders without smartphones or who do not speak English.

Johnson also noted that Somerville has seen reduced bus service for more than a year and questioned whether the bus will be able to handle the Green Line riders. But the T’s Lisa Battiston said the bus routes have sufficient capacity to carry would-be Green Line riders from Union Square.