Fits the profile of other late-1800s rail-to-road structures you and I have found. (John moreso than I, FWIW. I'll find a picture and within a month John will have the original location.)
I'm not sure exactly what to make of this...a 1967 Chicago, Burlington & Quincy track profile seems to indicate that this is a railroad maintained structure, built adjacent to a grade crossing (labeled G). In addition, the structure was there in the late 1930s:
http://ortho.gis.iastate.edu/client.cgi?zoom=1&x0=454760&y0=...
This would lead me to believe this is possibly a former railroad structure, and more research will be conducted. Also, I don't think I've seen a span like this where a vertical member is omitted between panels.
Visited this one today. Found it barricaded and the road closed at the railroad crossing, which was removed. Underneath appears to have clear evidence of railroad origins. I ran into a gentleman who works for the county road department further east who knew of the bridge, and mentioned it had been there his whole life and it may be demolished soon.