What action must a train take after entering a block on a proceed indication in CTC or manual interlocking limits when its speed is reduced below 10 mph?

When a train enters a block under a proceed indication in Centralized Traffic Control (CTC) or manual interlocking limits and its speed decreases to below 10 mph, it must proceed prepared to stop at the next signal until that signal is visible and displays a proceed indication. This requirement is grounded in safety protocols aimed at ensuring that the train is adequately prepared to react to any signals encountered, particularly if the train is operating at a reduced speed.

In this scenario, the train is entering a section of track where there may be limited visibility of the next signal. By proceeding prepared to stop, the train can ensure that it can halt safely if the next signal indicates a stop. This approach minimizes the risk of accidents and ensures adherence to established operational procedures.

The other options do not align with safety practices. Proceeding at full speed could lead to a failure to stop for a potentially critical signal, stopping and waiting for notifications may not be practical or safe depending on the surrounding conditions, and returning to the preceding block for instructions is not necessary when a clear procedure is already established for operating in these circumstances.