Sing it with me, everyone!
City of Winona has put up some close-up shots of decaying gusset plates in action on the MN43 bridge over the Mississippi River. Closing the sidewalk is clearly justified by these images.
There are several others on the City of Winona web site.
However, bikes STILL don’t belong on sidewalks, so they STILL could easily be allowed in the traffic lane. The bridge was never signed that bicycles could only use the sidepath (like on the Mendota Bridge of MN55), and MN43 was never a prohibited route (like most interstate highways). The restriction on cyclists appears to be a categorization failure – those making this rule are classifying bicyclists with pedestrians as sidewalk users, rather than as vehicles making shared use of the road as permitted under Minnesota Statute 169.222.