What does a four-digit train number signify?

A four-digit train number typically signifies that the train is cross-paired with another line. This is an important aspect of train operations, as it indicates that the train has a specific operational link to another train or service, allowing for coordinated schedules and connections. Cross-pairing is used to maximize efficiency and ensure that trains can share routes or provide seamless service to passengers transferring between different lines.

Understanding the significance of a four-digit train number is crucial for conductors and engineers, as it helps inform them about their train's operational context and routing. This knowledge can enhance communication and planning for timely operations.

The other options do not accurately reflect the purpose of a four-digit train number. Assigning a train to a single route, scheduling for maintenance, or indicating that it is a temporary service would use different identifiers or codes, rather than a standard four-digit train number, which is specifically used for cross-pairing identification.