What is the normal position of a derailing device?

The correct choice for the normal position of a derailing device is set to derail. The primary function of a derailing device is to prevent unauthorized or unsafe train movements onto a track, particularly in areas where trains should not be permitted to travel. By having the derailing device set to deride, it ensures that any train approaching will be redirected, reducing the risk of accidents and maintaining safety on the rail network.

This position acts as a safeguard, as it is positioned to disrupt the path of any train that approaches the area, thus protecting it from entering a potentially hazardous location. Typically, derailing devices are designed to be operated by authorized personnel only, ensuring that the safety measures remain intact until a valid reason for passage is established.

In comparison to the other provided options, the neutral position would not actively serve its purpose, allowing potential unsafe train movements. A position set to allow passage or closed would contradict the role of the derailing device, potentially putting safety at risk. Therefore, setting it to derail when not in use is a critical aspect of operational safety and adherence to railroad procedures.