When must switch points be secured from unintentional movement?

Switch points must be secured from unintentional movement before train movements in either direction to ensure the safety of train operations. This precaution prevents accidents that could occur due to unintended switching of tracks while a train is approaching or traversing the switch. Securing the switch points ensures that they remain in the desired position, which is crucial for directing the train safely along its intended path.

The other scenarios, such as securing after inspection, when a train is departing, or after the last train passes, do not comprehensively guarantee the safety that securing switches before any train movement does. If switch points are not secured prior to a train's approach, there is a risk of misrouting, which could lead to derailments or collisions. Therefore, the emphasis on securing switches before any movements is a fundamental safety protocol in railroad operations.