86th Street Overpass, Spanning Interstate 35 & 80 at Northwest Eighty-sixth Street, Urbandale, Polk County, IA

Significance: Built as part of the earliest construction on America's interstate highway system, the 86th Street Overpass represents a formative exercise in welded aluminum construction. It was designed by noted Iowa engineer Ned Ashton, under contract with the Iowa State Highway Commission, as an alternative to steel for bridge construction. The bridge's serendipitous merger of structural aluminum and electric arc welding was unprecedented. Never before had one structure combined such novel materials and techniques as this 220-foot-long overpass in Urbandale. Aluminum soon fell into disfavor among structural engineers, however, rendering the 86th Street Overpass an engineering anomaly. The lightweight metal may never have caught on for bridge construction, but the 86th Street Overpass remains an important milestone in civil engineering history: the first welded aluminum bridge in the world.
Unprocessed Field note material exists for this structure: N956
Unprocessed Field note material exists for this structure: N1517
Survey number: HAER IA-42
Building/structure dates: 1958 Initial Construction
Building/structure dates: ca. 1994 Demolished