The purpose of the door fault light is to ensure what?

The purpose of the door fault light is to ensure that all doors are closed for safety. This indicator is crucial for the safe operation of the train, as open doors can pose significant risks to passengers and crew. The light alerts the operator to any issues with the doors, enabling them to take necessary actions before the train departs. Ensuring that all doors are securely closed is not only a procedural step for safety but also a regulatory requirement that helps prevent accidents or injuries during transit.

While the other options touch on aspects of operation and safety, none specifically address the primary function of the door fault light, which is to monitor and confirm the closure of doors before the train can proceed. This indicator serves as a vital safety mechanism, ensuring the well-being of everyone on board.