Wiktionary
one-track
a. 1 (context of a railway English) having a single set of lines so that trains can run only in one direction at a time; single-track 2 limited to one idea or thought
Usage examples of "one-track".
They have one-track minds and too much imagination and there'll be some changes made.
At this range, even a Sidewinder might scoot past the target before its one-track mind could track on the MiG's exhaust and correct the missile's course, and if he dropped back for more room, the more maneuverable Fulcrum would give him the slip.
Cut-and-dried ideas, a one-track mind, harsh principles, and integrity, absolute integrity….
Pike Purcell had a one-track mind and that one track was busy with surmises over the story told him by Dud.