single track

Short definition from Wiktionary

Noun

1. 1
   Alternative spelling of singletrack.
2. 2
   A single rail line, where trains can only run in one direction at a time between passing points.

Adjective

1. 1
   Having only a single track so that trains may only run in one direction at a time.
2. 2
   Having a single curriculum or other educational approach for all students.