What is indicated by a green light on the C-3 exterior door lights?

Answer: C — Door Closed

A green light on the C-3 exterior door lights indicates that the door is closed. This signal is crucial for ensuring the safety and security of the train as it indicates that the train is ready for departure after an appropriate check of the door status. A clear understanding of these indicators is essential for train operation personnel, as they inform them whether it is safe to proceed. Proper recognition of a closed door contributes to maintaining the safety protocols necessary to prevent accidents, ensuring all passengers are secure before the train begins its journey.