New I-74 Mississippi River Arch Bridges

The Iowa-Illinois Memorial Bridge was once the crown jewel of the I-74 Corridor, the gateway to the Quad Cities region. The bridge spanned the Mississippi River and was a vital link to the seven-mile expanse comprised of bridges, interstates and communities. But times changed, and recent economic successes in the Quad Cities region  led to ever-increasing traffic demands, outgrowing the corridor’s existing infrastructure. The Iowa-Illinois Bridge became a major pinch-point for delays between the bi-state communities linked by the I-74 Corridor – Moline, Illinois and Davenport, Iowa. The Iowa and Illinois Departments of Transportation decided on an ambitious corridor improvement plan to alleviate congestion and sustain the regional economies. There were several objectives, including an increase in roadway capacities and designs for new roadways and interchanges. Most notably, the strategy called for the design and engineering of a new I-74 Mississippi River Bridge to replace the existing Iowa-Illinois Memorial Bridge.

Modjeski and Masters (M&M), as part of the Alfred Benesch design team, was tasked with providing final design services for the new I-74 Mississippi River Bridge. Located on a new alignment to the east, this is no ordinary crossing. The new I-74 Mississippi River Bridge features dual basket-handle arch bridges. First, our engineers employed analysis models and loading calculations to vet the conceptual design. Continuous coordination with the design team was equally essential, ensuring seamless integration of the design with the overall corridor plan. In the end, the bridge design met traffic demands and matched the service life of its predecessor.

During construction, M&M was also tasked with quantifying stresses from hangar cable vibration. To do this, engineers used instrumentation to monitor conditions for several months in all types of weather. The instrumentation consisted of 36 accelerometers, 8 lvdts, 2 string potentiometers, and a weather station. Resistance strain gages were also installed on individual wires of the hangers at 4 locations with adhesive.

Construction is now complete on the two river-crossing arches. The westbound span opened to traffic on November 13, 2020, and the eastbound span opened December 3, 2021.

The design of the new I-74 Mississippi River Bridge marks the return of M&M to familiar territory. In 1933, our firm designed the original Iowa-Illinois Memorial Bridge. We later twinned the structure in 1959.