Which term describes the safe system that uses interdependent signals and switches to prevent conflicting movements?

• A. Line-Of-Sight
• B. Automatic Block Signal System
• C. Pocket Tracks
• D. Interlocking

Answer: (D)

Interlocking is a safety system that coordinates signals and track switches so that routes cannot be set in a way that could cause a collision. The interlocking logic locks signals and switches together, so a signal can only show proceed if the corresponding route is safely established and there’s no conflicting movement. If another train could be on the same track or a different route would conflict, the system prevents that signal from clearing. This automatic interdependence eliminates the possibility of two trains being given conflicting indications at the same time, improving overall safety on the railroad.

Line-of-sight relies on operators to observe signals, which doesn’t automatically prevent conflicts. Pocket tracks are storage sidings for trains, not a safety system. An automatic block signal system manages train spacing by dividing track into blocks, but it doesn’t inherently interlock switches and signals to prevent conflicting movements the way interlocking does.