What identifies regular trains according to operational procedures?

The identification of regular trains in the context of operational procedures hinges on the leading engine number. This number serves as a unique identifier for each train, allowing for clear tracking and management of train movements within the system. By referencing the specific engine number, operational staff can quickly ascertain details about the train, such as its schedule, route, and any associated service information.

Using the engine number is crucial for operational efficiency and safety, as it ensures that all personnel involved in train operations can accurately communicate and coordinate based on a standardized, specific identifier. Additionally, the leading engine number helps maintain consistency in record-keeping and is essential for surveillance and troubleshooting any operational issues.

In contrast, while a train's destination, type, and frequency of service are all important aspects of train operations, they do not provide a unique and consistent method for identifying a specific train as effectively as the leading engine number does.