The Red Line train out of Braintree Station had already blown through three stops when the lights flickered out and the wheels slowly rolled to a stop.
Yet not a word of explanation had come from the conductor — for a very good reason.
When passengers looking for answers forced open the door to the operator’s cabin, nobody was there.
“We were all kind of, like: ‘What happened? Where is this guy?’ ” said Karrie Mohammed. By that time, she said, one passenger was in tears.
“We’re kind of — at this point — freaking out.”
In another embarrassment for the MBTA, a six-car, 420-foot Red Line train departed Braintree station Thursday morning with no one at the controls. The driver got out to deal with what he said was a signal problem, and his ride took off without him, officials said.
Governor Charlie Baker said the train controls “had been manipulated, which was why the train moved without a person controlling it.” What needs to be determined, Baker said, was whether the incident was because of negligence or something else.
Pulling out of Braintree around 6:08 a.m., the runaway train carrying about 50 people passed without stopping through the Quincy Adams, Quincy Center, and Wollaston stations on a 9-minute and more than 5-mile trip, before MBTA officials managed to stop it past North Quincy Station by cutting power to the third rail.
“We failed our passengers today,” Secretary of Transportation Stephanie Pollack said in an afternoon press conference that also failed to explain how, precisely, the MBTA lost its train.
Pollack said an investigation is focused on operator error but declined to give details or to name the driver at the press conference, though the T identified him as a veteran with more than 25 years of service. He suffered minor injuries when brushed by the train, T officials said. Another official with knowledge of the incident said the driver’s name is David Vazquez. No passengers were hurt, the MBTA said.
The runaway train caused significant commuter delays, which the T did not fully explain for several hours.
At 6:22 a.m., the MBTA Twitter account reported Red Line delays “due to a power issue.” No mention that officials had shut off the power to stop a runaway train with no operator. The T then tweeted an update, attributing delays to a “disabled train.”
“We dispatched the best information that we had at the time,” a T spokesman said Thursday night.
Bradley H. Clarke, a transit historian and president of the Boston Street Railway Association, said Red Line trains like the one that went rogue Thursday are operated in the cab by a device called a Cineston controller, which combines the accelerator, brake, and a “dead man’s” safety feature all in one lever.
“It’s called a dead-man’s controller, the idea being that if the operator dies at the wheel, he’ll relax his grip on the control handle, and the handle will pop up and stop the train,” Clarke said.
Though newer Red Line cars have a different system, he said, Cineston controllers have been in continuous use in transit systems for more than 70 years.
“They’re very reliable, very, very safe.”
Pollack declined to answer a question about whether the controller had been tampered with.
Many passengers waiting for the Red Line Thursday afternoon said they hadn’t heard about the runaway train, but their eyes grew wide when a reporter explained what had happened.
“Who would do that?” wondered Ronald Rae, waiting for a train at North Quincy station. “That’s pretty insane.”
Rider John Sweeney said the incident suggests something at the MBTA needs to be fixed, either at the highest levels or in the trenches.
“Something’s not working right, and I don’t quite know what it is,” Sweeney said.
Marjorie Donahue, waiting for a train at Wollaston Station, recalled the T’s service meltdown last winter.
“They don’t have very good reputations, and they’re making it worse,” she said. “If they can’t even handle this situation, then how are they going to handle a major blizzard?”
Officials explained Thursday that while the train was parked in Braintree, the driver reported a signal problem and requested permission to put his train into “bypass mode,” which allows the train to move even if it has not received the right signal. Trains occasionally operate in this mode, Pollack said, saying that it is safe under the proper procedures.
The MBTA, the Transit Police, the Department of Public Utilities, and the Federal Transit Administration are investigating, she said.
Stuart Spina, a member of the T Riders Union and a transportation researcher, said the bypass is a common move requested by subway operators to avoid having to sit excessively at a station in the event of a signal failure.
“It’s a pretty regular procedure, but this is the first time I’ve ever heard of a mishap like this happening,” he said.
Spina said he was mystified how the train could have accelerated without the operator in the cab, especially on a flat section of track.
“You need a person to push the throttle to move it,” he said. “That’s really the freakiest part of the whole thing, is how on earth could the train start moving?”
Moments after the train made its getaway, the driver reported the incident to an MBTA official at Braintree station, who immediately notified the MBTA’s Operations Control Center.
“We knew within 60 seconds, give or take 10 seconds,” Gonneville told reporters Thursday.
While the train was in bypass mode, the system’s automatic collision avoidance features would not have worked, he said. The T cleared other trains on the track, and then cut the power, he said.
Pollack said that trains in bypass mode are not supposed to be able to exceed 25 miles per hour, and that the investigation will try to determine how fast the train was going.
Toward the rear of the train, Sarah Sweeney, commuting to her job as a dental assistant downtown, had been scrolling through Facebook on her phone when the train stopped. With the lights out and the cold creeping in, the regular riders around her thought it was just another day on the oft-troubled line.
“We were actually joking about wishing we had coffee,” she said. “It just seemed like a normal Red Line problem. Luckily, no one in my car panicked, because I’m a panicker.”
Once the train stopped near North Quincy, T personnel boarded it and brought it to JFK/UMass Station, where passengers got off.
The T workers who entered Sweeney’s car were more upset than she was, she said. One “came crashing through,” asking whether everyone was OK.
The train was taken out of service and brought to a Red Line maintenance facility in South Boston.
The head of the MBTA’s largest labor union said the runaway train could have been stopped sooner if the MBTA had two workers aboard — as was the standard until a few years ago.
“If there was a second employee on the train, they would have . . . been equipped with the knowledge and ability to bring this train to a safe stop,” said James O’Brien, president of the Boston Carmen’s Union.
Waiting for the Red Line Thursday afternoon at Quincy Center, student Alex Feng, 16, put his head in his hand when he learned what had happened on the line that morning.
“I’ve got to tell my friends about that, because it’s absolutely insane,” said Feng, who said he takes the line every day to school.
Andy Rosen, Nicole Dungca, Laura Krantz, Matt Rocheleau, and Steve Annear of the Globe staff and Globe correspondent Alexandra Koktsidis contributed to this report. Mark Arsenault can be reached at firstname.lastname@example.org. Follow him on Twitter @bostonglobemark