Which order is likely to change frequently regarding train movements and safety?

The Daily Train Operations Bulletin Order (DTOBO) is the correct choice because it is designed to provide real-time information about train operations on a daily basis. This includes updates on schedules, track changes, and any safety-related instructions that may arise due to operational needs or conditions. Given the dynamic nature of train movements, the information contained in the DTOBO is frequently updated to reflect current circumstances, such as delays, maintenance work, or safety alerts. Consequently, conductors and operators rely heavily on it to ensure they are informed of the latest changes that could affect their routes and operations.

In contrast, the other types of orders may not change as frequently. General Orders typically encompass more broad and long-term policies. Operations Notices often address specific issues but with less frequency than daily bulletins. Bulletin Orders, while they may include important information, are usually less dynamic and more stable compared to the regular updates provided in the Daily Train Operations Bulletin Order.