A man was struck and killed by a commuter rail train on the tracks near Conway Park last night around 11:45 p.m., according to an MBTA spokesman.

Joe Pesaturo of the MBTA said it is not known why the man was trespassing on the railroad tracks. The man has not been identified. Transit Police, Somerville police, fire and EMS units responded to the scene. The incident is under investigation by Transit Police and the Middlesex District Attorney’s Office.