Which of the following describes the protocol for trains with authority to move in one direction when establishing working limits?

The correct choice is based on the understanding of how working limits function in a rail environment, particularly for trains with authority to move in one direction. When trains are given direction to operate with established working limits, the principle is to maintain safety and control over train movements.

Establishing working limits ahead of a train is crucial to ensure that any maintenance or other activities can be performed safely without the risk of a train infringing on those limits. The rule that a train cannot have more than one block of working limits ahead of them is grounded in the requirement to manage the operational area effectively while considering the train's direction and speed. This limitation is critical to ensuring a safe operational environment and preventing potential conflicts with other trains or ongoing work.

Therefore, this protocol is in place to maintain a safe separation between the trains and any maintenance activities or other trains operating in adjacent blocks. Expanding working limits beyond this could lead to dangerous situations with a lack of clear operational boundaries.