When non-signaled DCS rules substitute for ABS, how must trains be governed at interlockings?

The appropriate governing principle when non-signaled DCS rules substitute for ABS is that signals remain in service unless specified otherwise. This means that even when operating under non-signaled DCS (Direct Control System) rules, the existing signals at an interlocking location continue to provide guidance and indication to crews, unless there is a directive that states otherwise. This is important because it maintains clarity and consistency in train operations, ensuring that train crews can still rely on the information provided by signals to navigate safely through interlocking areas.

In contrast to this choice, the other options imply a complete disregard for signal indications or impose a blanket speed reduction or stopping requirement that does not reflect the operational flexibility and safety built into the rules surrounding signals and DCS operations. By allowing signals to remain in service, crews can operate with situational awareness and adjust their actions based on clear, visible indications, even in scenarios where non-signaled protocols are in effect.