= rack rail n. at rack, n.4 compounds.

a road running along the surface of the ground, as distinct from one which is elevated or underground.

a railway using rails of lighter construction than is usual, or than those on mainline railways, and intended to carry limited (esp. passenger)…

A switchback railway (in either sense); also transferred and figurative; applied in North America to a tight bend on an ascending road or trail.

a railway track having a rack rail as well as running rails; a railway which uses a rack and pinion locomotive system.

A single-rail track on which or suspended from which vehicles, machinery, etc., travel; a vehicle, camera, or other object that travels in this way.

a railway having the rails fastened by chairs to the sleepers.

A railway system operating on a monorail; the track of a monorail system.

= monorail, n. rare.