What type of speed must a train operate at when passing an interlocking signal with an ASC malfunction?

When passing an interlocking signal with an Automatic Speed Control (ASC) malfunction, a train must operate at Restricted Speed. This requirement is in place to ensure the safety of the train and its crew, especially in scenarios where the signaling system is not functioning correctly. Restricted Speed typically means operating at a speed that allows a train to stop within one-half the range of vision and to be prepared to stop short of any obstruction or stop signal.

This procedure minimizes the risk of accidents in cases where the ASC is compromised, preventing potential collisions and ensuring that the crew has full control of the train's movements. The use of Restricted Speed reinforces the importance of caution and preparedness in situations where normal operating conditions are disrupted.

In contrast, other speed options such as High Speed, Normal Speed, or Slow Approach Speed do not provide the necessary level of caution needed in the face of signaling issues, which underscores why Restricted Speed is the most appropriate choice in this context.