Federal investigators said Wednesday afternoon that the Green Line train that derailed in Cambridge earlier this month was traveling at a rate that far exceeded the designated speed limit when it went off the tracks.
The derailment occurred on Oct. 1 around 4:46 p.m. near Lechmere Station when the wheels of the lead trolley of the eastbound train left the tracks, causing the railcar to derail near Lechmere eastbound at the MBTA’s Red Bridge.
The National Transportation Safety Board, which released its preliminary report about the investigation Wednesday, revealed new details about the derailment, naming several factors that may have played a role, such as speed.
Less than a minute before the derailment, the train departed the station.
It was traveling at a speed of 36 miles per hour in a 10-mile-per-hour zone, the report said. The train then passed through a double red signal, which requires a stop, west of the Red Bridge.
It then “reached a switch [in the tracks] that was still moving,” investigators said.
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When the train passed over the switch, the “lead truck [roller] of its leading railcar continued straight, while the next two trucks of that same railcar took the diverging track and then derailed,” the report continued.
Approximately 50 passengers and two crew members were on board at the time of the derailment, the report said. Dozens were forced to evacuate and seven passengers were taken to local hospitals with minor injuries.
Visibility conditions were clear when the derailment occurred, investigators said. Damage estimates are still being determined.
Investigators began probing the cause of the derailment the following day, which involved conducting interviews, reviewing data from locomotive event records, along with security cameras and the signal system, and inspecting equipment and track conditions.
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Details of the preliminary report are subject to change.
The MBTA said in a statement on Wednesday that investigators affirmed the agency’s initial assessment that the “Green Line train operator was exceeding the posted speed limit at the time of the derailment.”
Following standard procedure after safety-related incidents, the operator of the train was suspended from service and currently remains out of service as the T’s safety department completes its own investigation, the agency said.
Operators who are determined to have violated the rules are disciplined, the T said.
“The safety and well-being of MBTA riders and employees are of the utmost importance. The MBTA has been working aggressively to improve safety at all levels and has stepped up its focus on compliance with operating rules, including adherence to posted speed limits,” the T said.
The National Transportation Safety Board said its investigation is ongoing, and that the next part of the process will focus on speed rules compliance and internal and external oversight.
The T, particularly the Green Line, has a history of derailments. This year, the agency scrapped an $83 million contract with a company in Germany to install crash prevention technology on the line, citing a lack of progress completing the job. Officials said they planned to find another vendor to install the technology.
Derailments of Boston subway cars with passengers have steadily dropped since 2019, when they peaked at 21, according to the T. There were two derailments in 2023 and three so far this year. Most derailments result only in delays, but in June 2019, at least 10 people were injured when a Green Line train went off the rails. It marked the third derailment that year.
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Shannon Larson can be reached at shannon.larson@globe.com. Follow her @shannonlarson98.