How should movement be governed if a fixed signal is absent?

When a fixed signal is absent, safety protocols dictate that movement must be governed by the most restrictive indication. This approach is essential to ensure the safety of train operations. In the absence of a clear signal, using the most restrictive indication helps prevent accidents by imposing the limits that would typically apply under more favorable conditions.

This practice acknowledges that there may be unknown factors or hazards that necessitate a cautious approach. The underlying principle is one of caution and prioritizing safety above all else. By adhering to the most restrictive signal, operators are effectively ensuring that their trains operate as if they are approaching a potentially dangerous situation, which may warrant reduced speed or stopping until further information can be ascertained.

The other options do not align with safety protocols: relying on the last known good signal might overlook changes in track or conditions that have occurred since that signal was displayed. Allowing unrestricted movement disregards critical safety measures and could lead to dangerous situations. Waiting for a visual signal from a conductor may introduce unnecessary delays and uncertainties that could be avoided with a strict adherence to restrictive indications.