This is likely the least busy upper Mississippi River crossing, at least the least busy of any crossing south of the Twin Cities. In fact, I was able to park on the roadway to take many of these photos. While the bridge is free today, it was a toll bridge until 1987, when the toll was 60 cents.
The photos below show a typical crossing, starting in Iowa, crossing the causeway into Sabula, exiting Sabula, following the causeway to the main channel of the river, and then crossing the main channel bridge. One question that I was left with is if there is a bridge or culvert allowing water to flow from one side of the causeway to the other leading into Sabula from the Iowa side of the crossing. The fourth photo below shows that there is in fact a small bridge in the causeway. This bridge is not easy to spot when driving across the causeway. The embankment in that photo behind the highway causeway is the railroad bridge causeway. That structure is more than a mile south of the highway causeway. This is an optical effect of using a long telephoto lens where the background is pulled closer to the viewer than it appears in nature.
The Iron Horse Social Club, a popular destination for motorcycle riders, is located on the east side of the river in Savanna, Illinois. As a result, many cycle riders cross the Savanna-Sabula Bridge. The steel grate bridge deck makes the half-mile long bridge a very memorable part of the trip. At speeds above 35 miles per hour, a bike will vibrate so badly that it becomes unstable. If you slow down below 20 miles per hour, the wheels are going slowly enough to drop into the small holes in the grate, which throws the front end from side to side. Even at 25 or 30 miles per hour, the front tire of a bike might oscillate back and forth 2 to 4 inches. As a result, many bike riders avoid this bridge.