What type of operational message remains effective until fulfilled or cancelled?

The correct answer is Bulletin Order (BO), as this type of operational message is specifically designed to remain in effect until it is either fulfilled or officially cancelled. Bulletin Orders are used in the transportation sector, including railroads, to communicate important operational instructions or rules that need to be followed.

This enduring nature of Bulletin Orders makes them crucial for ensuring compliance and safety in operations, as they are commonly related to changes in procedures, schedules, or safety protocols. Once the conditions outlined in the Bulletin Order are met or the order is formally rescinded, it ceases to be in effect.

In contrast, General Notices, General Orders, and Operations Notices have different purposes and may have time constraints or specific conditions under which they apply. General Notices typically inform personnel of important information without the enduring effectiveness, while General Orders can establish rules or procedures but may not necessarily remain in effect until fulfilled. Operations Notices often pertain to specific instructions or advisories, which can also have time limits or specific contexts for their relevance.