When can equipment that is blue flagged be coupled to or moved?

The correct answer is that equipment that is blue flagged can be coupled to or moved once a Blue Signal has been displayed. The Blue Signal is an important safety mechanism in railroad operations, indicating that work is being performed on the equipment and that it should not be moved until the signal is removed. The display of the Blue Signal ensures that workers in the vicinity are protected from accidental movement of the equipment while they are working.

Once the signal is displayed, it establishes a clear prohibition against moving or coupling the equipment. This promotes a safe work environment by alerting all personnel of the need to exercise caution and remain vigilant around the equipment.

The other options, while they address aspects of safety and operational procedures, do not capture the specific condition under which the blue flagged equipment can legally be coupled to or moved. It is essential to adhere to the presence of the Blue Signal, as any movement before its removal could lead to accidents or injuries.