A T train that coasted through four Red Line stations without a driver on board Thursday morning likely left Braintree Station unmanned after an operator error occurred, according to Stephanie Pollack, secretary and chief executive of the Department of Transportation.

About 50 passengers were aboard the driverless train when it left Braintree Station at about 6 a.m., traveling past North Quincy Station until transit officials de-powered the third rail and brought it to a halt. The MBTA, along with Transit Police, the Department of Public Utilities, and the Federal Transit Administration, are continuing to investigate the incident and the operator has been placed on administrative leave.


While no one aboard the train was injured, Pollack referred to the incident as “an unacceptable breach of our responsibility to keep our riders safe’’ during a press conference Thursday afternoon.

“We failed our passengers today,’’ she said.

The train’s operator was unable to start the inbound train due to a signal problem, and requested permission to put the train in bypass mode from the MBTA Operations Control Center, Pollack said. Bypass mode allows a train to depart from a station without receiving the usual signal, and requires the driver to toggle a switch on the outside of the train.

“Trains are put into emergency bypass mode only when there is a signal problem,’’ Pollack said. “It is a procedure that is used regularly, and it is a procedure that is used safely if proper procedures are followed.’’

MBTA officials cleared other trains along the track before shutting off the power, stopping the runaway train between North Quincy and JFK/UMass stations.

In a press conference earlier in the day, Gov. Charlie Baker said, “It’s pretty clear the main control that drives the train was tampered with. I think the big issue on this is whether it was a negligence issue or something else.’’


“It’s pretty clear that it was set in forward motion, which is why it moved in the first place when the signal was manipulated,’’ he said.

Pollack said Baker’s reference to possible tampering was based on an “early concern about whether the operator’s area of the vehicle was left in the condition it should have been when the operator exited the train.’’

Once the train was stopped, T personnel boarded the train and brought it to JFK/UMass, where passengers were asked to exit the train onto the platform.

A train operator was struck by the side of the train at Braintree Station and sustained minor injuries, the MBTA said.

When asked whether travelers should be concerned for their safety, Baker stressed that this was an “isolated incident.’’

Bill Brids, 53, was on the train heading from Braintree to his job at MIT when the T passed through a station without stopping. At first, he said, he thought the problem was a “rookie’’ driver.

“It was going very quickly through Quincy. I was shocked,’’ Brids said. “This thing was full throttle.’’

He said the train eventually started coasting and slowing to a stop. He was stuck on the train for about 40 minutes, and wasn’t told what had happened.

“I knew it was unusual,’’ Brids said. “I knew something definitely had gone awry.’’

T. Lee, another passenger who was on board, said in an e-mail to Boston.com that there was a conductor initially present at Braintree. After the train had stopped, MBTA employees told passengers that the train had no driver, Lee said.


“The scariest part was not knowing if there was a train ahead of us AND how this train would be stopped,’’ Lee wrote.

Mark Hohmann, 26, said he boarded an inbound Red Line train at Quincy Center at about 6 a.m. His train, which he now believes was just ahead of the conductor-less train, didn’t stop at North Quincy or JFK/UMass. Passengers hoping to get to those locations had to get off at Andrew and go back in the other direction, he said.

“They didn’t tell us anything,’’ Hohmann said, adding that there was “confusion’’ among fellow passengers.

Red Line trains were delayed for hours as a result of the incident. Service resumed on the Braintree branch about two and a half hours later.

Photos: These are the busiest MBTA stops

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