Rebecca Turco, Chris Lisinski, and Julianne Lima | Boston 25 News

“Problems with the MBTA’s new 4.4-mile Green Line Extension are so severe that the agency will need to widen more than two-thirds of the nearly brand-new tracks, officials announced Thursday, a stunning development that reveals construction and oversight failures.

MBTA General Manager Phil Eng, who was hired in April by Gov. Maura Healey, announced that an ongoing review determined roughly 50 percent of the Union Square branch and 80 percent of the Medford/Tufts branch will need to be ‘regauged’ to increase the space between the two rails.

Eng said he learned the extent of the problems ‘recently,’ but that other officials at the MBTA were or could have been aware about narrow tracks in 2021, or as early as 11 months before the first portion of the expansion opened to riders.

The problems appear linked to metal plates that connect the rails to the wooden ties that run perpendicular. Those plates—which were pre-installed off site before the rails were delivered to the MBTA—are too close together in many areas, Eng said.”