Recommended bridge type — August 2006
The process of a selecting a new bridge for the I-74 Mississippi River crossing has been underway since the early phases of the I-74 Iowa-Illinois Corridor Study project. Choosing a bridge type from the many alternatives that were developed is a significant decision and a variety of factors were considered. While aesthetics (how the bridge will look) was one component that was figured into this important decision, the river crossing itself has many features that dictate what type of bridge can effectively be constructed.
The bridge type selection process can be described in 3 phases. The first phase developed basic requirements such as the location of I-74 across the Mississippi River and the number of travel lanes required on the bridges. This phase was completed in early 2005. During the second phase of the bridge type selection process, the project team identified feasible types of bridges that satisfied the location, number of lanes and navigational requirements for the I-74 corridor. Based on the river crossing requirements the true-arch, the tied-arch and the cable-stayed bridge types were determined to be feasible.
Variations of these types of bridges were developed. Four bridge types were retained for further study and introduced to the public at the May 23, 2006, public information meeting as the finalist bridge types. The finalist bridge types presented at the public meeting were:
- The basket-handle, true-arch twin bridges
- The modified nasket handle tied arch twin bridges with vertical pier and vertical hangers
- The basket handle tied arch twin bridges with vertical pier and vertical hangers
- A cable stayed Ssingle bridge with a semi-fan cable arrangement
In addition to public input, engineering, financial and aesthetic considerations were addressed during the bridge type selection process, including:
- Public input: bridge type questionnaire results, general public meeting comment forms and comments received from the project Web site.
- Engineering performance: design features, constructability, environmental/social impacts, alignment/geometric compatibility, and security/protection.
- Financial performance: initial construction cost and life cycle costs.
- Aesthetics: structural logic (the bridge should look stable and appear to support its load with ease); visual relationship to communities (be a source of pride); the appearance of the bridge from the water, land and driver's perspective.