Final answer:
An emergency stop on a train can be initiated by passenger request, in addition to automatic triggers such as excessive speed, faulty brakes, or signal failure.
Step-by-step explanation:
On a properly maintained train, an emergency stop will not always result from excessive speed, faulty brakes, or signal failure, but may occur due to a passenger request. It is important to recognize that, although most emergency features on a train are triggered automatically by safety systems to prevent accidents, passengers also have the ability to initiate an emergency stop when necessary.
Regular commuters often become attuned to the intricacies of train operations, such as delays or track changes, which can be inferred from the behavior of the crowd without having to rely solely on schedule boards.