Which of the following books must employees maintain while on duty?

The requirement for employees to maintain the operating rules and timetable relevant to their duties is foundational to ensuring that they can perform their roles safely and effectively. This documentation provides critical information about signal indications, train movements, and other operational protocols that employees must follow to operate within the system safely.

Having access to these materials ensures that employees are continually aligned with the current practices and expectations of their job, reducing the risk of violations or accidents. The operating rules and timetable serve as a reference point and are essential for decision-making while on duty, enabling employees to respond appropriately to various operational scenarios.

While the other options may contain valuable information that could be beneficial for specific situations, they are not mandated for all employees to maintain while on duty in the same way that the operating rules and timetable are. Understanding and following the rules outlined in these documents is critical for compliance with safety regulations and overall operational integrity.