When is a highly visible marker required at the rear of every train?

A highly visible marker is required at the rear of every train from sunset to sunrise and in low visibility conditions to ensure that the train can be easily seen by other trains and vehicles, thereby enhancing safety. This requirement is particularly important during times when visibility is compromised due to darkness or weather conditions such as fog, rain, or snow. The marker serves as a warning signal that a train is present, which can prevent accidents and collisions.

Having visible markers at all times when visibility is low is crucial for maintaining awareness among train crews and nearby personnel. In contrast, options that suggest limitations based on time of day or specific weather conditions do not encompass the broader safety concerns that necessitate these markers to be visible at all times when visibility is compromised. This comprehensive safety measure is vital for preventing accidents, ensuring efficient operations, and protecting both personnel and the public near the railway tracks.