Built in 1929 on swampland by Chicago & Northwestern, Proviso was then the largest ayrd in the world, extending 5.5 miles east-to-west. At its peak in WWII classified between 7,000 and 8,000 cars a day, with an average of 128 manifest trains originated or terminated each day. The yard area also included a 58-stall roundhouse, an icing plant for refrigerator cars, and a 21-acre freight transfer house for less-than-carload traffic.
Today's Union Pacific yard has 30 receiving tracks, lying north-south, north of the hump, and 66 classification tracks, classifying over 2,000 cars a day, and originating 30 manifests (and handling 10 run-through manifests). The Chicago area's Global II intermodal facility is also located here.