“It appears to be a one-time human error,” said Daniel Grabauskas, the MBTA’s executive director of the commuter rail.

The derailment occurred on the Haverhill line around 8:20 a.m. as Train 208 went through a misaligned switch between Ballardvale Station in Andover and Wilmington Station, said Keolis spokesman Justin Thompson, resulting in “a slow speed, upright derailment of the two leading cars.”

Human error may have been to blame for the derailing of an inbound commuter rail train in Wilmington on Monday morning, transportation officials said.

Grabauskas emphasized that the train was traveling at “less than walking speed” when it happened and all of the cars remained upright on the track.


One passenger on the train reported hitting his head and initially declined medical attention, officials said.

The 400 passengers on that train had to be moved to bus shuttles at Ballardvale Station, and the incident affected other trains on the Haverhill Line as well. Passengers traveling on outbound trains from Boston had to be transferred to bus shuttles in Reading, officials said.

A crane was being used to lift the two derailed cars back into their correct positions on the track, and Keolis general manager David Scorey said he expected the work to be complete in time to allow for “normal evening service.”

Scorey said derailments don’t happen often. The last time one occurred on the commuter rail was January 2016, but there were no passengers on that train, Scorey said.

“It’s a very rare occurrence,” said Scorey.

Scorey said it doesn’t appear that defective or faulty equipment was to blame, and that the investigation is focusing on the manual operation of the switch.

“The investigation is ongoing,” he said.

Emily Sweeney can be reached at esweeney@globe.com. Follow her on Twitter @emilysweeney.