Why is a green flag never used to release a train from yellow-red flag requirements?

A green flag is never used to release a train from yellow-red flag requirements primarily because it does not signify the end of a restriction. This flag's purpose is not to communicate that it is safe to proceed without caution, rather, its use can be misinterpreted in situations where a signal is intended to indicate that specific operational restrictions are still in effect.

In the context of maintenance of way operations, flags are used to convey vital safety information. Color codes are established to maintain clarity and precision in communication among workers and train crews. The yellow-red flag indicates caution and the need to adhere to specific operating procedures due to ongoing work or hazards. Transitioning directly to a green flag could create confusion in the system where clear signals are necessary to ensure the safety of both personnel and the train.

Thus, keeping a consistent methodology regarding flag usage helps prevent misunderstandings or misjudgments that could potentially compromise safety. This adherence to protocol is fundamental in maintaining a safe working environment, which is why shifting from yellow-red to green without clearly indicating the release of restrictions deviates from the standard operating procedures established within the railway system.