Boston’s Orange Line commuter rail service carries an average of 201,000 riders every week, making it the second busiest line on one of the busiest metro rail networks in America. So, when the company that runs the service recently announced it was closing the line for 30 days to carry out repairs, it was a pretty big deal.

From August 19th, (MBTA) has closed the Orange Line service. For 30 days, engineers will work to improve the track and other infrastructure along the 11 mile route. :

The MBTA shut down the entire Orange Line on Aug. 19 and expects to resume subway service on the morning of Sept. 19. The unprecedented shutdown will allow the T to squeeze in five years’ worth of night and weekend track upgrades into 30 days, general manager Steve Poftak has said.

But since work started on the aging transit system, it hasn’t gone off without a hitch. On Monday, one of the trains carrying equipment for engineers derailed.

The Boston Globe reports that the “rear wheels of a stationary piece of construction equipment slipped off the rails” near Wellington station in the north of the city. Experts investigating the incident said rain could have caused “slick conditions” that could have contributed to the derailment.

A second incident happened Tuesday, when a piece of construction equipment derailed near the Massachusetts Avenue Station near the city center. A cause of that derailment has not yet been identified.

No injuries were reported in either derailment, and no equipment was damaged during the incidents. What’s more, the MBTA told the Globe that despite the setbacks, “neither one of these incidents will have an adverse impact on the Orange Line work schedule.”

Engineers working on the project have so far replaced more than 2,400 feet of rail, including on the southbound track between Downtown Crossing and State Street. This was one of six ‘slowdown’ zones that the MBTA was targeting in its work on the Orange Line.

The work has been a long time coming for the people of Boston. It was initially scheduled to begin in July, .

Last month, as it crossed a bridge after it caught fire. The fire was thought to be caused by a loose piece of metal that caught the track’s electrified third rail.