Until the 1980s, a regular feature of Highland railway operation - on the Kyle and Mallaig lines in particular - was mixed trains, where the locomotive hauled both passenger coaches and freight wagons in a single trainload.

This was a useful way of sharing haulage costs on lightly-trafficked lines, but the practice disappeared when loco-hauled passenger trains were displaced by more economic diesel units with engines slung under their floors.
(Permalink) David Spaven Kyle of Lochalsh Mallaig Mixed trains