How often can track bulletins be changed?

Track bulletins are essential for the safe operation of trains as they provide important updates and information regarding track conditions, work zones, and other critical safety issues. The frequency with which track bulletins can be changed is governed by established safety protocols and regulations.

The correct answer indicates that changes to track bulletins can only occur as specified by certain rules. This ensures that updates are made consistently and reliably, maintaining a high standard of safety across the railway network. These rules are designed to prevent unnecessary changes that could lead to confusion or mistakes among train crews.

Other options imply either unlimited changes or specific limitations that do not align with standard regulatory practices. For example, changing track bulletins at any time without restriction could lead to information overload or inconsistencies, while limiting changes to once per day or only when a new train leaves would not accommodate situations requiring real-time updates due to unforeseen circumstances. Therefore, the correct answer underscores the importance of adhering to structured guidelines for amending track bulletins.