Feds: Green Line driver pushed trolley to maximum power just before crashing into another trolley on Comm. Ave.

Update:WCVB reports the T is moving to fire the driver.

Federal crash investigators today announced the "how" of a July 30 trolley crash on Commonwealth Avenue, but are continuing to investigate the "why:"

In a brief report, the National Transportation Safety Board said:

The striking train accelerated to a speed of 31 mph before colliding with the train ahead of it that was moving about 10 mph. A preliminary review of striking train’s event recorder data revealed that the operat​​​or of the striking train placed the master controller in a full-power position prior to the accident.

The board, however, did not speculate on why driver Owen Turner did that:

The NTSB investigation is ongoing. Future investigative activity will focus on internal and external oversight, operational testing, crashworthiness of the equipment involved, and employee fitness for duty.