BOSTON (AP) -- Dozens of MBTA bus and subway drivers have been disciplined for using cell phones while on the job during the past three years.
  
Records obtained The Associated Press show that penalties for the drivers ranged from a day suspension to, in at least one case, the firing of a subway operator.
  
Use of a cell phone is considered a safety violation and is strictly prohibited by the MBTA.
  
Investigators looking into last month's fatal Green Line crash had focused on reports from passengers that driver Terrese Edmonds, had been using a cell phone before the accident.
  
Authorities have since concluded that Edmonds, who was killed in the crash, wasn't talking or sending text messages.
  
A call to the union representing MBTA drivers was not immediately returned on Saturday.