The Massachusetts Bay Transportation Authority Green Line trains collided near Agganis Arena at Boston University at about 6:15 p.m., according to the Boston Fire Department.
It was not immediately clear what caused the accident, which resulted in damage to the trolleys. Federal investigators from the National Transportation Safety Board will join the investigation into the cause of the crash, the NTSB announced Saturday on Twitter.
“The safety and well-being of our riders and employees is our chief priority,” the MBTA said in a tweet Friday night. “We take this matter extremely seriously and are actively investigating the incident to understand what occurred, and prevent it from happening again.”