Yellow-red flags are used to indicate what?

Yellow-red flags serve as warnings to train crews that they may be required to stop. This signaling is crucial for maintaining safety on the tracks, particularly in areas where conditions might change abruptly, such as near work zones or other potential hazards. When a train crew sees these flags, it prompts them to be alert, as they need to prepare for a possible stop that ensures the safety of both personnel on the ground and train operations.

In contrast, other options do not accurately reflect the purpose of yellow-red flags. For example, while slowing down may be necessary in certain situations, the specific function of yellow-red flags is to indicate the potential for a stop rather than just a reduction in speed. Being on schedule or the presence of workers involves different signals and procedures that are distinct from the warning indicated by yellow-red flags.