What type of warning system involves active monitoring for trains approaching a work zone?

The correct choice, individual train detection, refers to a system designed to actively monitor and identify the presence of trains approaching a work zone. This type of system uses various technologies, such as sensors or cameras, to detect train movements in real-time. Upon detection, it provides warnings to workers and other personnel in the vicinity, ensuring that they are made aware of potential hazards and allowing them to take necessary safety precautions.

This system is crucial for maintaining safety in environments where workers may be present on or near the tracks, as it allows for a dynamic response to train movements, rather than relying solely on static signs or manual monitoring. Active monitoring ensures that workers have up-to-date information about train schedules, enhancing their ability to work safely and efficiently in the designated area.

In contrast, the other warning systems like manual warning, electromechanical signaling, and passive warning signs do not provide the same level of real-time information about train locations. Manual warning may rely on personnel to communicate danger, while electromechanical signaling and passive warning signs can only alert individuals to static conditions rather than active train movements.