When are blue lights used instead of blue flags?

Blue lights are used in lieu of blue flags specifically at night to enhance visibility. This practice is crucial because blue flags serve as warning signals to indicate that work is being performed on or near the track, and their visibility is significantly reduced in low light conditions. By using blue lights at night, the safety of workers and train operations is maintained, ensuring that all personnel on duty are aware of nearby activities.

Utilizing blue lights during nighttime ensures that the warning signal remains effective and easily recognizable to train operators and other personnel. This allows for safer operations during hours when visibility is compromised.