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Arch Construction Milestone reached on I-74 Bridge Designed by Modjeski and Masters

MECHANICSBURG, PA | A significant milestone has been reached in the construction of the Iowa Department of Transportation and Illinois Department of Transportation’s new I-74 Mississippi River bridge. Earlier this month, the final keystone was put in place on the bridges’ Illinois-bound arch, completing construction of the Modjeski and Masters-designed basket-handle arch.

The keystone piece of arch weighs over 200,000 pounds and is 37 ft. long. With the last piece of the arch in place, construction will now shift to erecting the floor system that will carry the traffic lanes of Eastbound I-74. Once that is completed, both bridges will be open to traffic, dramatically increasing the capacity of the connection between these two states.

Modjeski and Masters, as part of the Alfred Benesch design team, provided design services for the two basket-handle arch bridges, which reach 230 feet above the Mississippi River. The new bridge will be more than twice as wide as the existing bridge, with four lanes in each direction.

The new bridge has been in the works for over two decades following a transportation study that revealed increasing traffic demands were outgrowing the current Iowa-Illinois Memorial bridge. The new bridge began construction in 2017 and is expected to be completed in 2022. The old bridge, also designed by Modjeski and Masters, will be demolished.

For more information about Modjeski and Masters’ work on the I-74 Bridge, visit

About Modjeski and Masters

Modjeski and Masters is one of the world’s leading bridge engineering firms, with a reputation for technical excellence and innovation that goes beyond current standards. Established more than 125 years ago, the firm is responsible for the design and maintenance of some of our nation’s most recognizable structures. Services include fixed and movable bridge design, inspection and rehabilitation, and all facets of life-cycle maintenance, research and code development. For more information, including in-depth videos of Modjeski and Masters at work, please visit

*Photo courtesy of

It’s been an honor to work with the IowaDOT and Alfred Benesch to improve the transportation infrastructure in the Quad Cities. The closure of the arches represents the culmination of many years of hard work by the team at Modjeski and Masters as well as all the other project members.  We are proud to have been part of the transportation solution that will allow many decades of future growth in the Quad Cities.

-Thomas Murphy, PhD, PE, SE,  Vice President and Chief Technical Officer at Modjeski and Masters