What is the minimum action required when encountering a blue light signal?

The minimum action required when encountering a blue light signal is to stop and await further instructions. A blue light signal typically indicates a situation that requires immediate attention from the crew, often related to maintenance work, an emergency, or other critical conditions that affect the safe operation of the train. Stopping ensures that the crew can assess the situation appropriately and avoid any potential hazards or unsafe conditions.

Proceeding with caution would imply that the crew can continue moving under the blue light, which could lead to misunderstanding the purpose of this signal. Similarly, backing up to the last signal or continuing at normal speed could jeopardize safety by not recognizing the significance of the blue light signal. The protocol to stop is crucial in maintaining safety and ensuring that the crew can receive necessary instructions before proceeding.