The I-129 bridge is a large steel plate girder bridge. A steel plate girder is a huge beam that is cut from a plate of steel, and then has reinforcing ridges and caps welded onto the plate. This allows the girders to be shaped as needed to carry large loads across long spans. The I-129 bridge feeds into an Interstate highway interchange on the Iowa side of the Missouri River. The bridge splits into three different branches, with the outside branches curving to the north and south to carry entrance and exit ramps from I-29.
The bridge is named after Sergeant Charles Floyd, a member of the Lewis and Clark Expedition. Floyd became ill in late July of 1804, and died on August 20, 1804 near the present day location of Sioux City. He was buried on top of a nearby bluff, which has been named Floyd's Bluff in his honor. A monument has since been erected on the sight, which overlooks the I-129 bridge. While it is not known what Floyd died of, it is commonly accepted that it was likely a ruptured appendix.