What must be applied to switches and signals leading to tracks used for movements on rusty rails?

Absolute blocks must be applied to switches and signals leading to tracks used for movements on rusty rails to ensure safety and control over train movements. Rusty rails can potentially compromise the integrity and reliability of the track's performance, making it necessary to implement a more stringent safety protocol.

The use of absolute blocks means that a section of track cannot be occupied by more than one train at a time. This provides a crucial layer of safety when navigating tracks that may not be in optimal condition, as it helps prevent collisions and accidents. By ensuring that only one train operates in a given block, dispatchers can more effectively manage movements, particularly in situations where the rail conditions are questionable.

In contrast, options such as double blocks or clear signals do not provide the same level of safety assurance necessary for rusty rails. Double blocks could still allow a potential for trains to occupy adjacent tracks inadvertently if not properly managed, while clear signals might give a false sense of security if the track condition is not stable. Therefore, the strict application of absolute blocks is warranted when dealing with potentially unsafe track conditions due to rust.