The Green Line train that derailed near Lechmere Station, sending several riders to the hospital earlier this month, was traveling 36 mph in a 10-mph zone, according to federal investigators.

The National Transportation Safety Board on Wednesday released its preliminary report of the ongoing investigation into the Oct. 1 derailment.

About 50 passengers and 2 crewmembers were on board as the train left Lechmere Station in Cambridge and headed east along the MBTA’s Green Line. Less than a minute later, the train derailed — sending seven riders to the hospital with non-life-threatening injuries.

“The train entered a 10-mph zone at 36 mph, passed through a double red signal (which requires a stop) west of the Red Bridge interlocking, and reached a switch that was still moving to direct the train into the diverging track as required by its route,” reads the NTSB report.

“When the train passed over the switch, the lead truck of its leading railcar continued straight, while the next two trucks of that same railcar took the diverging track and then derailed,” the report continues.

Visibility conditions at the time of the accident were clear. The weather was about 62 degrees, with no precipitation.

​While on scene, NTSB investigators completed interviews; reviewed data from locomotive event recorders, the signal system, and security cameras; and inspected railroad equipment and track conditions.

“The NTSB’s investigation is ongoing,” the report reads. “Future investigative activity will focus on speed rules compliance and internal and external oversight.”

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Parties to the NTSB investigation include the: Federal Transit Administration, Massachusetts Department of Transportation, Massachusetts Department of Public Utilities, MBTA, and Boston Carmen’s Union 589.​​

The derailment triggered a temporary closure on the Green Line between North Station and Medford/Tufts.

“We sincerely apologize for this incident and thank the public for their patience while we worked to resume service,” MBTA GM and CEO Phillip Eng said after the derailment. “Our thoughts continue to be with the riders who were aboard this trolley and those who were injured.”