A Green Line trolley may have been traveling at 30 mph when it struck the trolley in front of it Friday night, according to preliminary data recovered by the National Transportation Advisory Board.
The speed limit for that section of above-ground track is 10 miles per hour, according to multiple media reports.
The trolley that was struck was moving at 10 mph when it was rear-ended on Commonwealth Avenue, according to an NTSB statement released Monday evening. Both cars of the struck trolley derailed, along with one from the striking vehicle. Data on the trolleys speed, direction, braking and other measurements were preserved on recorders in each vehicle, the NTSB said.
The NTSB has had investigators on the ground since Sunday, and expects to file a preliminary report in 30 days.
The trolleys collided during Friday's rush hour, snarling traffic along Comm. Ave. as first responders and MBTA officials descended on the scene.
Twenty-seven people, including MBTA personnel, were injured and taken to local hospitals in the wake of the crash.
The operator of the striking trolley has been placed on administrative leave by the T.