This project is being sought to alleviate traffic on existing bridges linking Illinois and Missouri in downtown St. Louis.

The new bridge will be a cable-stayed bridge with three planes of cables and two single-pylon towers inclined nine degrees from the river and soaring 435 feet above the roadway. The structure will carry relocated Interstate-70 and Interstate-64 and will provide four traffic lanes plus two full shoulders in each direction, making it one of the widest bridges ever built across the Mississippi River at 222 feet. The overall length of the structure will be 3,150 feet and the main channel span, which will completely span the river and eliminate obstructions to river traffic, will be 2,000 feet long.

Modjeski and Masters initially prepared thirty bridge concepts for this project. Our firm conducted a detailed engineering and architectural bridge type study to determine the benefits and drawbacks of six of these concepts, including performance, affordability and aesthetics. With the selection of the preferred alternative complete, we are now performing final design.

Included in final design are details to enhance the security of the bridge which will be investigated and incorporated into the contract plans. This will include analyses and development of conceptual structural details to "harden" key components of the bridge at locations subject to unrestricted access.

Per direction from the FHWA, three tiers of protection will initially be studied using USACOE software, with the size of event (in terms of blast intensity) and the acceptable damage level (minimal to survivable) used as a means to distinguish the tiers. A cost estimate will be developed to determine the premium associated with increasing the security design criteria (or tier) the bridge will be designed to, and a summary report provided to the client for consideration and a recommendation.

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