What best describes double track in railroad terminology?

In railroad terminology, double track refers to two main tracks that allow for the movement of trains in opposite directions. This configuration increases capacity and efficiency on busy rail lines by enabling trains to pass each other without having to wait for a section of track to clear. It effectively reduces delays and improves the overall flow of traffic since trains can travel simultaneously in both directions.

The other options do not accurately describe double track. While two tracks operating in the same direction could technically exist, this is not what is meant specifically by double tracking, as it implies a simultaneous capability for bidirectional traffic. Additionally, the notion of alternating tracks for passenger trains or freight-only tracks does not align with the operational definition of double track, which emphasizes the main tracks' ability to support diverse train movements in both directions.