CS&SC = Chicago Sanitary & Ship Canal
Historic Bridges indicates this bridge was designed by Strauss Engineering instead of the City of Chicago.
If you can find a place to park, it is easy to take photos of railroad bridges from road bridges. But the converse is not true. So I'll use a satellite image.
The Cicero Avenue Bridge construction site on July 2, 1925, viewed looking north from the south side of the Chicago Sanitary and Ship Canal.
Dennis DeBruler According to Historic Bridges, the bridge was opened in 1927 with just two pony trusses. The third one was added in 1966 when the width was doubled. That is why the bridge looks so narrow in this photo.
That expansion must mean that the trusses were overdesigned by at least a factor of two because the center truss now holds the weight of a whole leaf rather than just half a leaf.