In this April 24, 2020, file photo, a Massachusetts Bay Transportation Authority Green Line trolley runs along Commonwealth Avenue in Boston. Credit: Michael Dwyer / AP

BOSTON — The Green Line train that struck a second train on Friday was traveling at 30 miles per hour, while the train that was struck was traveling at about 10 mph, according to a preliminary review of data by the National Transportation Safety Board.

The NTSB said Monday that the collision occurred on the Commonwealth Avenue rail grade crossing leading into the Pleasant Street Station, which is currently closed and under construction.

As a result of the collision, two cars of the leading train and one car of the trailing train derailed.

The striking train was traveling uphill, according to the NTSB.

Investigators were able to obtain data from the event recorder from the operating car of the striking train. The event recorder holds data regarding the operation of the train like speed, brake application, door positions and horn use.

The collision occurred at about 6:03 p.m. when the westbound MBTA Green Line train collided with the rear of a second MBTA Green Line train that was also traveling westbound.

One of four operators on board the two Green Line trains has been placed on paid administrative leave.

A spokesperson for the Massachusetts Bay Transportation Authority has declined to identify the operator, but said the decision was made Saturday based on developments in the ongoing investigation.

The operator was piloting the first car of the two-car trolley that struck the second Green Line train from behind. The operator has worked for the transit agency for seven years.

MBTA General Manager Steve Poftak said at a press conference Friday that the transit agency is reviewing the collision.

The Suffolk District attorney’s office is also looking into the collision.