County of bridge: Scotty County (Iowa) & Rock Island County (Illinois)
Location of bridge: I-74, over Mississippi River, between Moline (IL) and Davenport (IA)
Built: 1935
Design Engineer: Ralph Modjeski
"The Interstate 74 Bridge, officially known as the Iowa-Illinois Memorial Bridge, and often called The Twin Bridges, or the I-74 Bridge, is a pair of suspension bridges that carry Interstate 74 across the Mississippi River and connect Bettendorf, Iowa and Moline, Illinois. It is located near the geographic center of the Quad Cities.
"The bridge was designed by engineer Ralph Modjeski. The first span opened in 1935 as a toll bridge. In 1959, an identical twin span was added to satisfy increased traffic. The twin spans were upgraded to carry interstate traffic in the mid-1970s. Built for a daily crossing of 48,000 vehicles, the daily average is 80,000, making it by far the most traveled bridge in the Quad Cities. Both the Interstate 80 and 280 bridges are up to Interstate standards, while the Interstate 74 Bridge is functionally obsolete and was not built to Interstate standards, as it has two narrow lanes, no shoulder, and a 50 mile-per-hour (80 km/h) speed limit." ~ Wikipedia
Another great look, historically, at this bridge
"This is one of the most unique pair of bridges ever seen. So many different things make these bridges unique. First, these bridges visually appear to be absolutely identical. However, the northbound bridge was built in 1935, yet the southbound bridge was built decades later in 1960! Usually bridges built in 1960 have drastic differences between those built in 1935. Even the Grand Island Bridges, with a similar history and construction dates, have subtle differences in the design of the built-up beams. No such differences are apparent on the I-74 Bridges. It appears that the original plans for the 1935 bridge were simply taken out and used without any noteworthy changes to construct the 1960 bridge.
"Simply having two identical suspension bridges side by side is a unique feature. As such, an interesting place to view the bridges is in between the anchorages of the two bridges. This is a view that cannot be found anywhere else.
"The other unique feature of these bridges is the southern pony truss approach spans. From the road, these spans look similar to the stiffening truss. From below, these trusses have a haunched design at the piers. The trusses are continuous, adding to their technological significance. In between the pony truss spans and the suspension spans, there are deck truss spans. Additional deck trusses at this location in between the two bridges form a large plaza area on the bridge which is currently used for maintenance vehicles and utilities. There are also deck truss spans north of the suspension spans.
"The bridges include cable bents where the orientation of the cable changes near deck level and is directed straight into the anchorages.
"The 1935 bridge was built by the prestigious firm that was begun by famous bridge engineer Ralph Modjeski. At the time the 1935 bridge was built, the company had the name of Modjeski, Masters, and Case. Later and to this day the company is known became known as Modjeski and Masters. Perhaps unsurprisingly, Modjeski and Masters was the company hired as the consulting engineer for the construction of the 1960 bridge. The contractors for the 1935 bridge included McClintic Marshall Company for the superstructure and Kansas City Bridge Company for the substructure. The contractors for the 1960 bridge included the Bethlehem Steel Corporation for the superstructure, the Dravo Corporation for the substructure, and the Valley Construction Company for the approaches.
"The bridges display classic details that are shared with many suspension bridges associated with Ralph Modjeski. These include towers with large "X" patterns except at the top where horizontal beams interrupt the pattern. The use of pony truss stiffening is also common among his bridges.
"The bridges are very aesthetically pleasing, from the tower design, to the graceful lines of the suspension system. The pony truss stiffening introduces a geometric complexity to the bridge, further enhancing the aesthetics of the bridge.
"Both bridges should be considered historically and technologically significant examples of suspension and truss bridges that were also built by a noteworthy engineering firm. The 1935 Bridge is further significant for association with Depression-era relief funds. The plaque for the bridge
"The plaques for the bridge are currently located on a monument in the northeast quadrant around the bridges in a small park. This is not the original location of the 1935 plaques and monument, and the 1960 plaques have been added to the monument. This monument may move again when the historic bridges are replaced." ~ Bridge Browser