At what speed must a train proceed if the previous signal indication is unknown?

To ensure safety when a train's previous signal indication is unknown, it must proceed at restricted speed until the leading wheels have passed the next governing signal. This approach is crucial because it allows the train crew to maintain control and be prepared to react to any unexpected conditions, such as a stop signal or an obstruction ahead. Restricted speed allows the train to stop within a short distance, ensuring the safety of the crew, the train, and any surrounding infrastructure.

Operating under the assumption that the signal ahead is clear could lead to dangerous situations, especially if there are unreported or unknown signal aspects that could indicate the need to stop. Additionally, moving at high speed to minimize delays is contrary to safety protocols, as it increases the likelihood of accidents if a stop becomes necessary. Simply proceeding based on a clear area also does not consider the importance of signals in railway operations and can result in safety oversights.