Photo: A current MBTA bus that fits under the commuter rail tunnel at Belmont Center.

The fleet of new buses purchased by the MBTA since 2017 will “help fulfill its environmental needs while increasing transit service,” according to the mass transit public agency.

The 350 hybrid Xcelsior vehicles manufactured by New Flyer of America are cleaner and far more fuel-efficient than the all-diesel buses being replaced, can hold more commuters, and best of all, will “provide a more comfortable ride for passengers.”

And they’re too tall to clear the Commuter Rail tunnel in and out of Belmont Center.

When the T took an XDE40 model for a spin to Belmont in the fall of 2019, it was discovered that the height of the new vehicles could not travel in the right-hand lane as it passed on Concord Avenue without taking off the top of the bus on the underside of the tunnel’s ceiling.

“The negative for Belmont and a handful of other communities that have this type of a bridge feature on their routes is the bus is too tall to get under the bridge,” said Glenn Clancy, director of the Office of Community Development and the town’s engineer before the Select Board this week.

The issue facing the T is the design of the commuter rail tunnel is a barrel vault which is a self-supporting arched form. Because the tunnel’s height diminishes as it curves to meet the supporting walls, a large vehicle that can successfully pass under using the middle of the road does not have the same clearance remaining on one side of a typical two-way road.

“I was at the MBTA in December and the new buses came up in conversation,” said Clancy. As a result, “the [MBTA bus lines are] not going to enter Belmont Center anymore.” The bus lines impacted are numbers 75 and 74.

The news couldn’t come at a more disadvantaged time for commuters as the new buses will come into service “at a June-ish timeframe,” said Clancy.

For the faithful commuters who board the bus at the layover site adjacent to the Belmont Fire Station at the corner of Leonard and Alexander Avenue, the new buses will require riders to hike about a quarter-mile to a pair of proposed replacements stops and layover locations.

“[Town Administrator Patrice Garvin and I] were tasked with trying to find a new location for a layover. So working with the MBTA … we looked at some of the concepts and … there are two places where it would make sense: either in front of the Lions Club or in front of the First Church in Belmont, Unitarian Universalist on Concord Avenue across the street from the post office,” said Clancy.

But both locations have their own challenges. While the Lions Club site would be more convenient for commuters as they would not have to cross either busy Common Street or Concord Avenue, there’s this little thing called the Christmas tree sale, a more than 70-year holiday tradition that starts the Saturday after Thanksgiving and lasting until Christmas day week.

“I see that as one of the real civic functions that it’s a high profile thing that happens in the town. I don’t want to be known as the guy who resulted in the Lions Club not having this function every year,” said Clancy.

As a result, Garvin and Clancy had a conversation with a couple of members of the club stating their concern that the buses could make it by the club’s operation for the five weeks of the sale. Their response was positive.

“They’ve assured us that they can do that,” said Clancy.

But what determined the new location was an MBTA requirement a potential layover location would be long enough to accommodate two buses. The Unitarian Church has the space between their driveway curb-cuts while it would be a stretch at the Lions Club and along Royal Road.

Clancy said the First Church site has pedestrian access with the crosswalk in front of the post office, and while it would have been more desirable in front of Lions Club because there is a pedestrian underpass at the Lions Club, “we’ve settled on the [First Church] location to do this.”

“The T has already sent the bus out they’ve already made the route (which will require the bus to make a right-hand turn, loop around the WWI Memorial, and take a left onto Common towards Cambridge). They know they can make the turns so everything is great in that regard,” said Clancy.