What must be done when a train crosses over to or obstructs another track?

When a train crosses over to or obstructs another track, it is essential to protect the move as prescribed by rule 99. This rule outlines the procedures necessary to ensure that the movement is conducted safely and that other trains or personnel are aware of the obstruction. The protection measures might include setting up warning signals, communicating with nearby crews, and ensuring that the area is clear of any conflicting movements.

This ensures not only the safety of the train in motion but also protects the integrity of the surrounding railway operations. By adhering strictly to these protocols, the risk of accidents or miscommunication is minimized, thereby maintaining operational safety and efficiency. The other choices do not meet the comprehensive safety standards required in this situation.