Dive summary:

• It wasn't in the initial plans, but a replacement bridge over the Mississippi River at Hastings, Minn., but the design that the state Department of Transportation approved yielded the longest unbraced freestanding arch bridge in the United States.
• The design, which involved fabricating the bridge off-site and then floating it to the location on barges, came from Parsons Corp. as the design partner in a venture with Lunda Construction Co. and Ames Construction Inc. and was allowed because the state said it would look at alternative concepts if they fit its goals of a 100-year design life, ease of maintenance and redundancy.
• The design uses post-tensioned concrete ties at either end of the arches, although temporary steel ones were used for the trip from fabrication to placement in order to reduce weight.

From the article:

"By doing that, not only did we create an iconic bridge, we combined the cost-effectiveness of the approach with aesthetics," says Vincent Gastoni, Parsons' principal bridge engineer.  ...