How long must blocking devices restricting access to temporary restrictions be held?

The correct answer indicates that blocking devices restricting access to temporary restrictions must be held until the Dispatcher confirms receipt of the restriction. This is essential for ensuring safety on the rail network. Holding the blocking devices until the Dispatcher acknowledges the restriction provides an additional layer of communication and ensures that all parties involved are aware of the changes and can operate accordingly.

This procedure is vital for preventing accidents or misunderstandings that may arise if a train were to approach the area without the appropriate precautions being communicated. The Dispatcher plays a critical role in managing and overseeing train movements, and their confirmation serves as the official recognition of the temporary restriction.

The other options imply different durations for holding the devices, but they don't encompass the critical aspect of effective communication and confirmation with the Dispatcher that is necessary for maintaining safety protocols. Holding the blocking devices indefinitely or only until the train arrives or passes may lead to situations where essential information about the restriction is not securely communicated, potentially compromising safety on the rail line.