Final answer:
The best initial action for a train operator noticing arcing is to ensure safety by notifying the control center, deenergizing the electrical system, and following emergency procedures as required.
Step-by-step explanation:
If a train operator notices considerable arcing underneath the train car while stopped at a station, the best initial action is to ensure the safety of the passengers and crew.
The operator should first notify the control center about the issue so that appropriate safety protocols can be initiated. It is crucial to deenergize the electrical system of the train if possible, to prevent further electrical hazards or damage to the train's systems.
The operator may need to follow specific emergency procedures which often include stopping the train service, evacuating passengers if necessary, and awaiting further instructions from the technical maintenance team.