That new Green Line branch to Union Square? The T is closing it for 42 days this summer.

A train pulled into the new Union Square MBTA station on August 6, 2022.Carlin Stiehl for The Boston Globe

Green Line service between Lechmere and Union Square stations — the first segment of the long-awaited Green Line Extension, which opened just over a year ago — will be suspended for more than a month starting in July, the T announced Thursday.

Service will be suspended from July 18 to August 28, according to the T, while MassDOT crews undertake “critical repair work” on the Squires Bridge, which runs over the tracks to Union Square station.

The T is encouraging riders to instead utilize bus routes 86 and 91, transferring from the Washington Street at New Washington Street bus stop to the East Somerville station on the E branch, from which regular Green Line service will still operate. Riders can also take the Route 87 bus from Lechmere to Somerville Avenue at Stone Avenue stop, near Union Square.

Lisa Battiston, a spokesperson for the MBTA, wrote in an email that shuttle bus service is not being considered since “existing bus options are all less than a 10-minute trip” and “riders may choose to walk between East Somerville and Union Sq for Green Line Medford Branch service, which is about a 10-minute walk.”

Jarred Johnson, executive director of TransitMatters, said the T has “got to do a better job” on communication, especially when it comes to transparency and getting information to riders.

He said 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.

“Information has been spotty, wayfinding and signage has been missing or just bad,” Johnson said of previous closures. “There needs to be somebody responsible for these diversions.”

He noted that Somerville has already seen reduced bus service for more than a year.

“Are they confident that the bus will be able to handle this?” Johnson asked. “Is there going to be any attempt to try to coordinate the bus schedule with the train?”

Battiston added that the bus routes have sufficient capacity to carry would-be Green Line riders from Union Square.

Jacquelyn Goddard, a spokesperson from MassDOT, wrote in an e-mail that the bridge repairs will target “specific, localized areas of 6 steel beams that have deteriorated” and are necessary for maintaining the integrity of the bridge.

The 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 beams, according to Goddard.

Union Square station, along the D Branch, was the first segment of the Green Line Extension to open, following a 1990 promise by the state to extend the Green Line to “Ball Square/Tufts University” and a more than 30-year push by advocates and officials. The remainder of the extension, which will not experience the 42-day interruption, opened in December.

Further outbound, the Green Line’s B Branch will also be closed from July 17 to July 28, as MBTA maintenance crews replace rails, ties, steel plates, and asphalt.