When must train crews notify the dispatcher regarding their on-duty period?

The correct answer indicates that train crews must notify the dispatcher three hours before their duty ends. This requirement is crucial for maintaining safety and operational efficiency. Notifying the dispatcher well in advance allows for appropriate planning and scheduling of relief crews, ensuring that there are no gaps in service and that fatigue management protocols can be adhered to.

This advance notice also enables the dispatcher to anticipate crew availability and make any necessary adjustments to train operations. It reflects the importance of proactive communication in the railway industry, where timely decisions can enhance safety and service reliability.

The other options do not align with the established protocols for notifying dispatchers. For example, notifying the dispatcher immediately after beginning a shift might not provide sufficient time for managing crew changes before their duty ends. Similarly, waiting until issues arise or only notifying an hour before legal limits expire could lead to operational disruptions and safety concerns.