What does a white light waved up and down by a flagman signal to a train?

The signal of a white light waved up and down by a flagman indicates that the train should proceed with caution towards a green lantern. This type of signaling is commonly used in train operations to communicate with engineers about the condition of the track ahead or other pertinent alerts.

The waving of the white light specifically conveys that the train is clear to continue, but the need for caution ensures that the engineer remains vigilant for any potential hazards or further instructions that might not be visible from a distance. The green lantern serves as a positive indication of a clear track ahead, but approaching with caution allows for the safe assessment of any unforeseen circumstances that may arise.

Recognizing the significance of these signals is crucial for safe train operation, as they facilitate communication between on-ground personnel and train crews, ensuring that the train can proceed safely while being prepared for any required adjustments.