these pictures and description of the Merrian Street Bridge in Minneapolis are courtesy of Gerald Kackman:

These photos of a King bridge in Minneapolis, the Merriam Street Bridge. This bridge crosses the east channel of the Mississippi River between Main Street and Nicolet Island. The span was originally part of a multi-span bridge crossing the Mississippi at Broadway St. a couple of miles upstream from it's present location. Some years ago the Broadway Street Bridge was replaced and this span was saved, floated down the river on pontoons and installed at Merriam St. The bridge decks are now concrete but when it was at Broadway St. the vehicle lanes were open steel grids and I think the walkways were wood planks.

-- Gerald Kackman