What must trains operating with a malfunctioning ASC apparatus do at signals?

When trains are operating with a malfunctioning Automatic Speed Control (ASC) apparatus, the primary safety concern is to ensure that the train is controlled and does not exceed speed limits or run past signals inappropriately. Stopping at all signals is mandated as a precautionary measure. This approach ensures that the crew can manually assess the situation at each signal and take the necessary actions to proceed safely based on the current conditions and signals displayed.

By requiring trains to stop at all signals, the regulation prioritizes safety over the potential risk of continuing to operate without the protective function of the ASC. This condition helps avoid potential accidents that could arise from misinterpreting signal indications while operating without an operational ASC.

The other choices do not uphold safety standards under these circumstances. Following signals without stopping could lead to violations of signal indications that the crew may not be able to adequately respond to without the ASC's support. Similarly, proceeding at maximum speed, or relying on hand signals, would not provide the level of control required for safe operation in the context of a malfunctioning ASC.