What must a train dispatcher do when a signal is disregarded?

When a signal is disregarded, the train dispatcher must instruct the crew to stop and hold until further instructions. This action is critical for maintaining safety and preventing potential accidents. Disregarding a signal typically indicates that a train has failed to comply with important directives meant to protect both the train and its surroundings. By ordering the crew to stop, the dispatcher ensures that the situation can be assessed appropriately before any further movement occurs.

This protocol helps to minimize risks associated with potential track obstructions, other trains in the vicinity, or unsafe conditions that could lead to collisions or derailments. Communication is vital in these situations, and stopping the train allows for a thorough evaluation and the opportunity to provide the crew with updated instructions on how to proceed safely.

In contrast, other options suggest actions that could lead to unsafe conditions, such as allowing the train to continue without addressing the disregard of the signal or changing the signal to green, both of which could exacerbate risks on the railway. Such measures would undermine the safety protocols that are in place to protect all parties involved.