The Massachusetts Bay Transportation Authority is entering the home stretch with its Orange Line repair blitz, with the embattled transit agency having taken the unusual step of shutting down the Boston area's second-busiest subway line for a month in order to cram in years of needed work.

As of Sept. 8 the MBTA had completed 66% of the repair work planned for the Orange Line, an MBTA spokesperson confirmed.

Service on the line is slated to resume as planned on Sept. 19, having been shut down on Aug. 19 in order to perform estimated five months of work into a single month, officials have said.

“We remain positively confident about getting this work done and getting this work done on time,” MBTA General Manager Steve Poftak told reporters at an update Tuesday at the Community College station.

To date, 7,000 linear ft of track along the Orange Line has been replaced, according to the MBTA spokesperson, with two of six speed restrictions on the line now lifted as well. Crossovers have also been replaced at the Ruggles and Forest Hills and stations as well, a move that should boost reliability of the line.

The agency now has up to 60 new Orange Line cars (for a total of ten full train sets) available for service once the Orange Line resumes service, the spokesperson, Joe Pesaturo, said in an email.

The MBTA's big push to repair the Orange Line comes amid a recently completed review of its operations by the Federal Transit Administration that followed a series of accidents and mishaps on the system’s various subway lines.

On July 21, a fire brought an Orange Line train to a stop on a bridge over the Mystic River, prompting passengers to break windows in order to escape, with one passenger jumping into the river and swimming to the shore during the incident.

In April, a Red Line rider was dragged to his death when his arm became caught in the door of a subway car as he was exiting the train.

Serious Problems, Serious Response

“It will be the longest service diversion overseen by the [MBTA] for an entire line … replacing what would have taken five full years of weekend and evening diversions,”  Mass. Gov. Charlie Baker (R) said at a press conference announcing the temporary Orange Line shutdown in August.

Two major contractors are leading the Orange Line overhaul, with work going on around the clock and with 150 to 175 construction workers undertaking repairs at various sites along line at any one time, said Pesaturo.

Barletta Heavy Division is handling Wellington state yard track and signal upgrade under a $9.5 million contract, and signal upgrades at the Oak Grove and Malden stations under a separate, nearly $14-million contract, according to information provided by Pesaturo.

Middlesex Corp., under an estimated $13-million contract, is doing emergency track repair work aimed at areas of the line where conditions have led to speed and capacity restrictions. The work includes replacing rail ties and rails, “ballast and resurfacing repair of rail anchor systems, and cleaning of track bed drainage systems,” according to a description provided by the MBTA.

Meanwhile, the shutdown of the Orange Line for an entire month has scrambled the daily lives of hundreds of thousands of commuters. MBTA officials turned to the commuter rail system, which services some of the same stops, while bringing in 200 buses to plug service gaps.

The MBTA’s fleet of emergency buses, provided under a contract with A Yankee Line, Inc., has cost $37 million.