Which set of items must be stated in single digits as mandatory directive numbers?

• A. Authority number
• B. Engine number
• C. All numbers contained in the body of the directive
• D. Authority number, engine number, and all numbers contained in the directive

Answer: (D)

The key idea here is standardizing how numeric identifiers are conveyed so they’re clear and unambiguous during transmission and recording. In a directive, the numbers used to identify who issued the directive (the authority number), which locomotive or engine is involved (the engine number), and any other numbers that appear inside the directive all need to be stated using single-digit forms. Doing this consistently helps crews read back and verify the directive accurately over radio or on paper, reducing chances of mishearing or miswriting multi-digit numbers.

That’s why the best answer includes all of these elements: the authority number, the engine number, and every number contained in the directive. Limiting the requirement to only one part wouldn’t guarantee that every crucial numeric identifier is presented in the same clear, single-digit format, which could lead to confusion during operation.