Railroads. Freight and passenger train service unit costs (selected expense accounts) of class 1 steam roads in United States, including proportion of mixed-train and special-train service (compiled from 164 reports representing 180 steam roads, switching and terminal companies not included), Dec. 1921 and 1920, and 12 months [ended with Dec.] 1921 and 1920; [prepared in] Bureau of Statistics.