Thanks for the additional information. I visited and photographed the bridge in 2008, but I was not aware of its past history as a major route carrier.
This bridge is the original crossing of the River to River Road, Iowa Primary Road 7, the Detroit Lincoln Denver Highway, and finally US 32 before it and Kellogg were bypassed when 32 was paved in 1928.
Executive Director Iowa Division
Route 6 Tourist Association