Which of the following unusual occurrences must be reported to the train dispatcher?

The requirement to report collisions and derailments to the train dispatcher is rooted in the principle of safety and operational integrity within railway operations. Such events can have severe implications for not only the operations of the railroad but also for the safety of personnel and the general public.

When a collision or derailment occurs, immediate reporting allows the train dispatcher to take the necessary steps to mitigate further risk, manage the movement of other trains in the area, and coordinate a response that may include emergency services. This reporting is critical not just for immediate incident management but also for investigation and future prevention measures.

While routine maintenance checks, weather changes, and upgrades to equipment may be important in their own right, they typically do not necessitate immediate emergency actions or intervention from a train dispatcher the way that a collision or derailment would. The latter represents a significant deviation from safe operational practices, which is why it must be prioritized in reporting protocols to ensure a swift response and ongoing safety for all railway operations.