One of the new Orange Line cars derailed as it traveled slowly through Wellington rail yard Monday afternoon, according to a MBTA spokesman.
The car was not in service and no passengers were aboard at the time of the derailment, Joe Pesaturo, a spokesman for the Massachusetts Bay Transportation Authority, said in a Monday e-mail.
The train came out of service at noon after carrying passengers through the morning, he said, and as the train slowly moved through the yard, the last of its six cars came off the rail as it passed over a track switch.
The cause of the derailment is under investigation, and an inspection found no significant damage to the vehicle, Pesaturo said.
The track switch in question is slated to be replaced as part of $102 million in improvements to the Wellington yard, Pesaturo said.
A half-dozen new Orange Line cars debuted in August, the first of 152 that will by 2022 replace the fleet of decaying, decades-old cars still plying the line.
The transit agency pulled two new Orange Line trains from the tracks on Sept. 20, after a door panel — known as a leaf — opened on a single car while the train was in motion.
The T said the train stopped automatically when this happened, but the incident prompted an investigation into what went wrong.
During its investigation, the MBTA learned that a component on the door, called a “bump stop,” had malfunctioned. This led the transit agency to replace the same piece of equipment on all 144 doors of 12 new cars.