A train filled with passengers that left a station south of Boston Thursday morning without an operator was being investigated as a case of operator error, officials said.
The Massachusetts Bay Transportation Authority said the runaway Red Line train took off from Braintree Station without its conductor at approximately 6 a.m. Thursday morning.
The train passed four stations before the MBTA depowered the third rail, bringing the train to a stop just past North Quincy Station roughly nine minutes after it first departed, MBTA Chief Operating Officer Jeff Gonneville said at a press conference Thursday afternoon.
"Operator error is the current focus of the investigation," Massachusetts Department of Transportation Secretary Stephanie Pollack said, adding that the extent to which the operator was responsible would be determined by the investigation. The MBTA did not release the name of the operator.
The incident began when the operator was unable to start the train Thursday morning due to a signal issue, Pollack said. The operator was cleared by the MBTA Operations Control Center to put the train into emergency bypass mode.
The operator then exited the train to finish that procedure, but that's when the train left the station, she said.
"Trains are put into emergency bypass mode only when there is a signal problem," she added. "It is a procedure that is used regularly and safely when appropriate procedures are followed."
Those procedures, Gonneville said, include putting the train on full service brake and using a hand brake before exiting the cabin. The operator then walks down to the front of train and pulls a switch to initiate the emergency bypass mode, he said.
"So part of the investigation will be to understand whether that occurred," he added.
Authorities were initially looking into a report that "a safety device in the train's cab may have been tampered with," the MBTA said in statement released earlier Thursday.
Fernanda Daly, a passenger on board the train, told The Associated Press that the lights went out when the train was stopped and passengers rushed to try to open the doors and press the an emergency button in the train car.
"There were people even trying to break the windows so we could get out," she said.
Passengers in the first car attempted to knock on the door of the cabin and discovered they were on a train without a conductor, Daly said.
None of the roughly 50 passengers on board reported any injuries, Pollack said at the press conference. An MBTA employee was struck by the train and suffered a minor injury, according to the AP.
The MBTA has asked Transit Police detectives to investigate the incident.
"Passenger safety is the highest priority for the MBTA and this highly troubling incident is under investigation by Transit Police detectives," MBTA General Manager Frank DePaola said in a statement.