Final answer:
The main reason for train crew to announce the cause and duration of delays is to inform and provide transparency to passengers, thereby managing their expectations and maintaining trust.
Step-by-step explanation:
The bulletin states that the main reason for making an announcement about the cause and probable duration of a train delay is to inform passengers. Keeping passengers informed minimizes uncertainty and frustration among them, as they can adjust their plans accordingly and understand the situation better. When regular passengers sense a delay due to cues such as the movement of the crowd, not everyone has the same level of experience or intuition about these situations. Therefore, clear communication from the crew is essential for all passengers, providing transparency and maintaining trust.