Single-line working

On a railway, single-line working[1] refers to the practice where, when one line out of the two lines is blocked, trains are able to use the other in either direction.[2] This is usually when a line is out of use for maintenance, or because of damage, obstruction or train failure.

Single Line Working
An example of single track working:
The left track is not being used
whilst the right one is
An example of single-line working: maintenance of way crews are working on two tracks (left) of a three-track line in the Czech Republic while a passenger train passes on the third track (right) in 2011.