A Green Line trolley motors through a ceremonial ribbon pulled across the track at the brand-new Lechmere Station on Monday, March 21, 2022. The event celebrated the start of service on the Green Line Extension's Union Square branch. Photo by Chris Lisinski | State House News Service

Gov. Maura Healey on Wednesday called a dramatic slowdown of the Green Line Extension “incredibly frustrating,” but declined to provide any details about how the nearly brand-new tracks fell into such poor condition so quickly.

The MBTA last week disclosed that it had slashed speeds on the Green Line Extension to 3 miles per hour in some stretches because the rails were recently found to be too narrow to safely support full-speed travel.

Officials have not explained the shocking development about narrow tracks or indicated why previous inspections did not identify any problem.

“The situation with the Green Line Extension, I’ve talked about this before, is incredibly frustrating. It appears that – well, I’m not going to speculate right now,” Healey said Wednesday when asked about the Green Line Extension at an unrelated event. “I will tell you, as I told you last week, that I have directed GM [Phil] Eng to get to the bottom of what happened in terms of actual work and the contracts. We are on that. We are, importantly, right now making any needed repairs as quickly as possible, so that we can get those trains moving as quickly as possible. But we’ll be back with more on that.”

The Green Line Extension’s two branches opened last year to great fanfare and events headlined by former Gov. Charlie Baker.

A spokesperson for the Department of Public Utilities, the state agency responsible for MBTA safety oversight, said last week that the MBTA, DPU, Federal Transit Administration and consultants all certified the new branches were compliant with safety standards before operations began.

However, the Boston Globe reported Tuesday that the FTA does not actually conduct safety certifications for projects and instead works to ensure agencies like the MBTA have sufficient procedures in place to keep their own work safe. An FTA spokesperson told the Globe the T itself certified the track system, including the gauge between tracks, and that the DPU concurred with the MBTA’s certification.