|Richard Fiedler shared|
Wabash bridge at Hannibal, MO
Richard Fiedler There are notes on the bottom right that gives that insight. Says "changing draw span". Thanks for filling in the mystery Bill.
Judging from a satellite image, they moved it all the way to the west. It has since been replaced with a lift bridge which creates a wider navigation channel. Note that the truss span for I-72 for the navigation channel is also on the west side.