What must derails be when the track is not in use?

Derails are safety devices designed to prevent unintended train movements onto tracks that are not in use, such as sidings or other areas. When the track is not being utilized, the derails must be positioned safely to prevent any possibility of a train inadvertently rolling onto that track. This leads to the requirement for derails to be in specific positions for safety purposes.

When derails are in the locked position, they remain secure and cannot be easily altered, providing assurance that the track is safely closed off from any rolling stock. Being in the derailing position means that they will actively guide any trespassing vehicles off the main track and onto a safe area. Furthermore, being in the lined position for non-derailing ensures trains can safely traverse areas without risk of derailment when the tracks are indeed in use.

Therefore, all three conditions must be fulfilled when the track is not in use, confirming the necessity of derails in the locked, derailing, and lined positions for non-derailing purposes. This comprehensive approach underscores the importance of derails for maintaining safety and preventing accidents.