When does an operating mode change occur while entering yard territory?

An operating mode change occurs when the front of the train enters yard territory because this is the point at which specific rules and procedures applicable to yard operations take effect. Yard territory typically has distinct operating rules to ensure safety and efficiency, differing from mainline operations.

Upon entry into the yard, the train moves from regulations that govern high-speed operations on the mainline to rules that dictate lower speeds, increased caution, and potentially stop-and-start operations within the yard. This shift in operational protocol is crucial for managing the risks associated with yard activities, such as working around other trains, switching movements, and loading or unloading cargo.

The other options do not appropriately mark the transition into yard territory. For instance, simply reaching the station does not account for the broader implications of yard operations, and waiting for a signal to change speed does not signify the entry into yard territory—rather, it could be a part of mainline rules still in effect prior to entry. Lastly, awaiting instruction from a trainmaster indicates a protocol-based decision but does not inherently mark the moment of transition between operational modes.