The Main Drainage Channel of the Sanitary District of Chicago is crossed by 3 railroads. The Pittsburg, Cincinnati, Chicago and St. Louis; Chicago Terminal Transfer and the Chicago Junction Railways. The first having the western four tracks and the others having the next two each easterly tracks. Making a total of eight tracks crossing the channel. From this is derived the name of the structure. --Journal of the Western Society of Engineers--
Two western spans no longer in use.
They would have been operated during World War II for sure, since the nearby Western Avenue Bridge was retrofit into a lift bridge at that time and it is far higher than the RR bridges. Not sure when the S&S canal ceased to have operable bridges. I do know that these RR bridges have the lowest clearance of all bridges on the S&S Canal. Many scrapes and bends are visible on the underside of these bridges from barges that were too tall.
I wonder what the last time this bridge was 'opened'? I'd bet it's been a while.