A Double track railway usually use one track in each direction, compared to a single track railway where trains in both directions share the same track.

In the earliest days of railways in the United Kingdom, most lines were built as double track because of tha difficulty of co-ordinating operations prior to the invention of the telegraph.

In the earliest days of railways in the United States, most lines were built as single track for reasons of cost, and very inefficient timetable working systems where employed to prevent head on collisions on single lines. This improved with the development of the telegraph and train order working.