What happens if the flashing mode indication is not acknowledged within the allotted time?

When the flashing mode indication is not acknowledged within the specified time frame, the protocol is to apply the service brake and bring the train to a halt. This procedure is a crucial safety measure put in place to ensure that the train does not continue to operate under potentially unsafe conditions. It acts as a fail-safe to prevent accidents that could arise from a lack of acknowledgment, which could indicate that the engineer is not able to respond appropriately due to various reasons such as distraction or incapacitation.

In contrast, the other possible outcomes, such as proceeding to the next stop, adjusting speed, or merely logging a warning, do not ensure immediate safety for the passengers or the train's operation. The primary goal of halting the train with a service brake application is to maintain safety and control over the train operation in case of an acknowledgment failure.