During the subway flagging procedure, what type of signal arrangement is critical to monitor?

In the subway flagging procedure, monitoring the lights in a flagging arrangement is critical as they serve as essential signals to communicate the status of the track and train operations to operators and crew members. These lights are used to indicate whether trains should proceed, stop, or proceed with caution in situations where normal operations are disrupted, such as track maintenance or emergency situations. Proper visibility and understanding of the flagging lights ensure that operators can respond appropriately to changes in track conditions, thereby enhancing safety and preventing accidents.

While warning signs, alarm systems, and train schedules also play important roles in train operations, they do not specifically provide the real-time visual signals needed during the dynamic situations encountered in flagging procedures. Warning signs convey information regarding potential hazards, alarm systems alert operators to specific issues, and train schedules guide operational timing, but none of these actively regulate the immediate train movements in the way that flagging lights do.