Factual error: Filbert is in the southwest corner of PA. It is very far out of the way of Harrisburg and completely off the route from Philadelphia to Harrisburg.
Factual error: There are no tracks, stations or train routes in Filbert, PA.
Factual error: The cars the train is pulling for the Philadelphia to Harrisburg route are not ones that represent any passenger cars used for the Amtrak or Keystone routes. They are SEPTA cars on an undisclosed route, other than the Harrisburg line.
Answer: If such an event were to actually occur in the real world, that would be the most likely scenario. The mass suicide is just how M. Night Shamylan chose to portray the event in his film.