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Highways, Byways, And Bridge Photography
Iowa-Illinois Memorial Bridge
I-74 Mississippi River Crossing At Davenport
Davenport, Iowa

Iowa-Illinois Memorial Bridge

Northbound Span
• Structure ID: NBI 000000000047280 (IA), 000081990117701 (IL).
• Date Built: Dedicated November 18, 1935.
 
Southbound Span
• Structure ID: NBI 000000000047290 (IA), 000081990117702 (IL).
• Date Built: Opened January 20, 1960.
 
Statistics Common To Both Spans
• Location: River Mile 485.8.
• River Elevation: 561 Feet.
• Highway: I-74.
• Daily Traffic Count: 71,100 (2003).
• Bridge Type: Pure Suspension, 2 Parallel Spans.
• Length: 5,148 Feet Overall, 740 Foot Longest Span.
• Width: 24 Feet, 2 Lanes Per Span.
• Navigation Channel Width: 710 Feet.
• Height Above Water: 66 Feet.
While these two bridges look identical, one span is actually 24 years older than the other. Twin suspension bridges are rather rare. There are a pair of parallel suspension bridges crossing the Delaware River that claim to be the longest such pair in the world. There is a pair of bridges north of Oakland where one in the pair is a suspension bridge. And the new Tacoma Narrows 2nd span will be a suspension bridge, as is the existing span, but they will look different when completed.

Despite being upgraded in 1975 to handle Interstate grade traffic, these two bridges once again are facing the end of their useful life. There is simply too much traffic demand for the four narrow lanes. To make matters worse, there are no shoulders and merging lanes are short. The two state departments of transportation have been looking at upgrading the I-74 corridor in the Quad Cities area. A preferred alternative highway was selected in 2005, and a preferred alternative bridge was announced in 2006. All that remains is to find funding. The new bridge will be a pair of rainbow arch bridges. The arch will start right at the waterline, with the highway cutting through the arch about one third of the height of the arch. Each bridge will have three full width lanes, and two interstate-grade shoulders.

A question often arises in how you measure the length of a bridge. In the case of these two bridges, one could argue at least a dozen different numbers for the bridge length. In looking up the National Bridge Inventory, we find that Iowa thinks that the bridges are the same length at 3,371 feet each, but Illinois thinks that they are of different lengths, 5,018 and 5,149 feet long. None of these numbers appear to match the bridge itself. For example, the suspended section is a total of 1,480 feet long. The river crossing is 3,380 feet wide. The total amount of bridge that is elevated off of the ground from end to end is nearly 9,390 feet, almost 2 miles. Some also would argue levee to levee, but that is hard to do since Bettendorf does not have levees. In this case, one number that describes the bridge is impossible to come up with. Rather, one has to pay attention to the bridge details, and these two bridges have a remarkable suite of details to examine.

In the upper photo, we are looking downstream to the south. The nearest span is northbound, which makes it the older bridge.

Iowa-Illinois Memorial Bridge
Iowa-Illinois Memorial Bridge
Iowa-Illinois Memorial Bridge
Iowa-Illinois Memorial Bridge
Iowa-Illinois Memorial Bridge

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