MA: The Green Line gone dark: Peek underground as the MBTA replaces wooden beams from the 1890s

The wooden beams that ran along the ceilings of the MBTA’s Green Line tunnels were installed when the line was built in the late 1890s, a decade before the Ford Model T was released and Oklahoma became the 46th state in the Union.

And for the next nearly 130 years, the beams capably served Boston’s transit system. Although most riders never noticed, the beams — known as “troughs” — provided a crucial barrier between electrified train wires and the tunnel ceiling overhead.

But the time has come for them to take a well-earned retirement.

Years and water damage left their mark on sections of the trough, and the wood posed a fire risk, MBTA officials said. Federal and state officials made clear last year that the troughs needed a modern replacement.

They were “degraded,” but still safe and functioning, MBTA Chief Operating Officer Ryan Coholan said at a public meeting Thursday. Still, “it’s a 130-year-old piece of wood underneath Boston Common ... The day it decides to bite us, it’s going to significantly impact our service.”

The replacement project has been no small feat, as Green Line riders have surely realized. It required shutting down the line’s four branches across the entirety of Downtown Boston from Dec. 8–22 to give maintenance crews unencumbered access to the train tracks.

Working around the clock for two weeks, crews replaced 13,000 feet of trough with a modern equivalent that will “outlast all of us,” Coholan said.

The work is scheduled to wrap up Monday, on schedule, before the Green Line reopens Tuesday morning.

Maintenance workers packed the tunnels, wearing reflective vests and hard hats plastered with stickers proudly touting the always-on-call reality of their jobs.

This project had been planned for a year, T officials said. Executing it required extensive coordination to move heavy equipment and materials into the tunnels in the proper order, power down the trains’ electric grid, organize shuttle bus service for riders impacted by the shutdown and much more.

Beginning at North Station, the shutdown extended as far west as Allston and Fenway. It covered some of the most heavily trafficked subway stops on the MBTA, including North Station, Park Street and Copley.

The T has embraced a “bite the bullet” strategy on projects that require such widespread disruption to normal operations, choosing to complete as much work as possible in one fell swoop.

A two-week closure was the least disruptive way to schedule the work, Massachusetts Transportation Secretary and MBTA General Manager Phillip Eng said last month.

Maintenance crews have piggybacked off the shutdown to finish other crucial projects, including installing the new Green Line Train Protection System, a network of transponders that will warn train operators of potential collisions and speeding.

On Thursday, at Boylston station under the Boston Common, crews also installed new steel beams to support the Green Line tunnel ceiling in areas where water damage had deteriorated the existing beams.

On the streets overhead, riders who would otherwise take the Green Line instead boarded shuttle buses the T offered as a free, alternative mode of transport during the shutdown.

Other riders packed the Orange Line, which runs roughly parallel to the Green Line through Downtown Boston, or took commuter rail or public buses.

The wooden troughs stayed in place for five generations because the T had long delayed investing in its replacement, Eng said last month. Replacing them was “vital.”

“It’s a result of the need to take care of things more timely, and we’re committed to doing that,” he said.

The Green Line moved about 50,000 riders on an average weekday in November, according to data collected by TransitMatters, a public transportation advocacy organization.

“This was really, really important,” Coholan said. “We appreciate the patience of the public. We know this is impactful.”

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