n. a dirt road used by four-wheeled vehicles rarely enough that their tires have made ruts that became parallel singletracks.
Two main tracks, one of which the trains run in one direction and the other in the opposite direction.
Two parallel main tracks.
Two main tracks, on one of which the current of traffic is in a specified direction, and on the other in the opposite direction.
A double track railway usually involves running one track in each direction, compared to a single track railway where trains in both directions share the same track.