What characterizes a controlled signal?

A controlled signal is characterized by being managed and regulated by a Rail Traffic Controller. This means that the signal's indications are specifically set and monitored based on real-time traffic conditions, allowing the controller to maintain safe and efficient train operations throughout the rail network.

The role of the Rail Traffic Controller is crucial, as they analyze various factors, including train locations, speeds, and allowable movements, to determine when and what signals to display. This centralized control helps ensure that trains are safely directed through various sections of the track and assists in preventing collisions or accidents.

In contrast, other options do not accurately describe the nature of a controlled signal. For instance, while signals may be designed to display indications for multiple tracks, the defining characteristic of 'controlled' revolves around oversight and management by a human operator rather than the scope of its display. Weather conditions can influence train operations, but a controlled signal operates independently of those factors, focusing instead on immediate traffic management. Lastly, while signals may be used in yard operations, they are not exclusive to that context, as controlled signals are also vital in mainline operations to manage train flow safely.