Work on the Green Line Extension missed an internal target for the second time in several months. But the T says the project is still on pace to meet its target of completion by December 2021.

The original project schedule called for existing commuter rail tracks to be shifted by September, but officials over the summer set a new target of Nov. 15 as they cited "schedule pressures." Once complete, the movement of the Lowell Line tracks will create space for new Green Line tracks to be built.

However, MBTA spokesman Joe Pesaturo told the News Service that the effort is still in progress more than a month after the reframed target.

"The track shift work began in September and continues this month and is scheduled for completion early next year," Pesaturo wrote in an email. "While the track shift work is being completed, station work is underway along the GLX alignment. As with the overall track shift, the sequence of critical activities is reviewed and updated over the duration of the project's implementation."

Pesaturo said a "significant segment" of the track was shifted this month, and "critical station work" will take place in 2020 after completion of the step. However, he said the project "remains on schedule to be completed by the end of 2021" according to its original timeline.

Officials will provide a more detailed update to the Fiscal and Management Control Board at the board's Jan. 13 meeting, according to Pesaturo.