Final answer:
Plug doors on a railcar must be closed and locked securely before the train starts to move to ensure passenger safety. The interlock system in place prevents the train from moving if the doors are not properly closed.
Step-by-step explanation:
The doors of a railcar equipped with plug doors must be closed before the train starts to move. This is essential for the safety of all passengers aboard. Plug doors are designed to seal by sliding into the doorway and then moving laterally to close the opening completely, providing a secure closure. These doors have an interlock system that prevents the train from moving if they are not properly closed. For this reason, they must always be closed and locked securely while the train is in operation, including when it is stationary at a platform but ready to depart.
In a railcar equipped with plug doors, the doors must be closed when the train is in motion. This is to ensure the safety of the passengers and prevent any accidents or injuries. When the train comes to a stop, the doors can be opened again to allow passengers to exit or enter the railcar.