Dina Rudick/Globe Staff
The MBTA says it has determined that a broken wheel caused the derailment Tuesday afternoon of a Red Line train leaving Alewife Station.
MBTA officials said one of the eight metal wheels on the fourth car of the six-car train cracked and a doughnut-shaped piece of steel fell off.
The officials said they have been moving quickly to try to figure out why the wheel broke and making widespread inspections to look for signs of possible similar problems. None have been found, said Anna M. Barry, director of subway operations.
Sixty-five people were evacuated after the derailment, which happened as the train was leaving the station Tuesday night. Nobody was injured.
The T has had several problems in recent weeks, including a Green Line train derailment on Dec. 13 near Copley Square and problems with a 40-foot wall on the Red Line on Monday at the Porter Square station. Officials said the Green Line incident was caused by human error and the wall problem was due to the system's aging infrastructure.
The Alewife derailment is "completely unrelated to anything else that has happened," said Barry.
T spokesman Joe Pesaturo said there was one common thread in the two Red Line incidents: "The T acted swiftly in both cases to make sure the riding public was safe."
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