Metropolitan Transportation Authority (MTA) Assistant Conductor Practice Test

The function of a derail is to redirect a train off the tracks in a controlled manner, primarily as a safety measure to prevent potential accidents. When discussing the correct choice, the definition fits well because a non-interlocked derail is a fixed device attached permanently to the rail. This type of derail is designed to activate when a train approaches at an unsafe speed or in an unintended direction, ensuring that the train is intentionally directed off the track, thereby avoiding disasters such as collisions or derailments on the main track.

It's important to note that this device is not temporary, as it needs to be strategically placed and maintained as a permanent feature of the railway infrastructure. The other choices do not accurately pertain to the primary function of a derail. For instance, a temporary device to stop trains might imply methods like signal systems or emergency brakes, which differ significantly from the intended application of a derail. Tools for track repairs serve a different purpose entirely, focusing on maintenance rather than safety containment. A warning signal for approaching trains relates to alerting personnel rather than controlling train movement. Understanding these roles helps clarify the specific purpose and necessity of a derail within the rail system.