What is one of the duties of a tower operator regarding flagging trains?

The primary duty of a tower operator regarding flagging trains is to ensure that all signals are clear. Clear signals are essential for safe train movement, as they communicate to train crews whether it is safe to proceed or if they need to stop. This involves monitoring and managing the signaling system, ensuring that signal aspects reflect the correct information for the trains that are approaching or departing from a station or junction. By ensuring all signals are clear, the tower operator helps maintain safety and efficiency in train operations, preventing accidents and facilitating smooth train movements.

The other options, such as providing refreshments or conducting safety briefings, are not typically part of a tower operator's responsibilities. While expediting services is important in the rail industry, it is secondary to the primary focus on safety, which is achieved through proper signaling.