What defines a main track in railway operations?

A main track is defined as a track through yards and between stations that requires authority to occupy. This definition is essential in railway operations because it signifies that the main track is the main route for trains traveling between major points, such as yards and stations, and is regulated to ensure safe and efficient movement. Occupancy of this track is controlled through proper authorization, which is critical to prevent collisions and maintain proper scheduling for train movements.

The other choices do not capture the essential characteristics of a main track. For instance, a track used exclusively for freight trains, a service track for maintenance staff, or a temporary construction track do not serve the broader operational role of facilitating general train movement through key locations on the railway. The main track's designation and requirements around occupancy are crucial for maintaining safety protocols and operational efficiency on the railway network.