Sentence:  They served the industries located along the tracks, performed such freight-house switching as became necessary, set cars off or put cars on passenger trains when necessary, lined up <WSD>fill-outs</WSD> for through-freight trains, made up the locals originating at Idaho Falls, and set cars off and put cars on the through freight trains 277 and 278. 
Meaning of the word marked with <WSD> tags:  An extra car added to a freight train in order to achieve a minimum tonnage.