A passenger surveys the views as Somerville gives way to Cambridge aboard a Green Line train headed from Union Square to Lechmere Station on the first day of expanded service Monday, March 21, 2022. Photo by Chris Lisinski | State House News Service

The MBTA resumed running trains on the Green Line Extension at full speed on Tuesday following a string of overnight maintenance efforts that involved physically pushing the tracks apart to restore an appropriate width.

MBTA officials announced Wednesday that about a mile’s worth of slow zones had been lifted across the Green Line Extension’s Union Square and Medford branches, just a bit more than two weeks after the sudden revelation that trains were limited to 3 mph because of rails that were too close together.

At first, it was unclear what work the agency had performed to allow trains to resume full-speed travel, but an MBTA official told the News Service that crews spent several recent nights widening sections of the rails to address the narrowness problems.

The official, who communicated only on background, likened the process to resetting a door hinge. Workers removed screw legs holding down rail tie plates, then repositioned those plates. They then placed a device in between the two rails that forced the loosened side to move about a quarter of an inch, bringing the gauge between the track to a standard distance, the official said.

MBTA officials still have not disclosed how the tracks – some of the newest in the entire system – became too narrow to safely accommodate full-speed travel for several weeks. General Manager Phil Eng said last month that the problem only appeared on a recent inspection, not prior scans.

It’s particularly unusual because rail gauges typically widen, not narrow, over time, officials and experts have said. The official who spoke on background said allowing trains to run at full speed on narrow tracks “squishes the wheels.”
Asked at an unrelated event Wednesday morning for an update, Eng said the investigation is “still ongoing.”

“We’re investigating everything right now with regards to that project, with regards to how this came about, and when I have that information, I’ll share that,” he said. “Everyone deserves to hear that.”

Eng, Transportation Secretary Monica Tibbits-Nutt and other officials were spotted heading into a meeting Wednesday afternoon in Gov. Maura Healey’s State House office. More than an hour later, they exited through a different door than they entered and declined to speak with reporters on the way out.

A Healey press aide told reporters Eng was unavailable to answer questions and referred to his remarks earlier in the day.

Crews had more time to conduct the repair work on the Union Square branch of the Green Line Extension, which closed on Sept. 18 to allow the Department of Transportation to make repairs on a highway bridge that crosses over the tracks. That project wrapped up two days early, and Green Line service in the area resumed Wednesday.

On the Medford branch, MBTA workers had to limit the track-widening work to overnight hours.

The T official said crews only got a chance to access affected areas shortly before 3 a.m. and needed to finish their work by about 4:20 a.m. each night because of safety measures that limited their time on the rails. Several crews were deployed to repair narrow tracks, breaking off to address multiple areas at once, the official said.

Both branches of the extension opened last year to great fanfare and celebrations from elected officials, including then-Gov. Charlie Baker.

A spokesperson for the Department of Public Utilities initially said the MBTA, DPU, Federal Transit Administration and consultants all certified the Green Line Extension met safety standards before it began running.

The DPU later clarified to the Boston Globe that the T itself certified the extension, including the gauge between tracks, and the department concurred. The FTA has since said it does not conduct its own safety certifications for individual projects.