Under what condition can multiple unit trains operate at 60 mph in the event of an ASC failure?

Operating multiple unit trains at 60 mph in the event of an Automatic Speed Control (ASC) failure is permitted when authorized by the Train Dispatcher. This is crucial because the Dispatcher has the overall responsibility for train movements and the safe operation of the railroad. By granting authorization, the Dispatcher is ensuring that all safety protocols and operational considerations have been taken into account in that specific situation.

This authorization typically includes a thorough assessment of the current conditions on the track, including occupancy and any potential hazards, ensuring that the trains can proceed safely despite the ASC failure. It serves as a form of positive control to maintain safe operations, allowing for optimal decision-making in emergencies.

In contrast, the other conditions listed, such as guidance by cab signals while ignoring the ASC failure or operating under other less authoritative measures, do not provide sufficient safeguards or systematic oversight which are critical in maintaining safety during such irregular operations.