Historic Bridges

Details

The Kittyhawk Avenue Bridge is one of a series of riveted Warren pony trusses built in Carroll County in 1913; it is the prototypical example of what would become an Iowa State Highway Commission standard design. The bridge carries a secondary county road over an unnamed field stream some three miles southwest of Carroll. The structure consists of a 50-foot, rigid-connected Warren pony truss, supported by a timber substructure. According to Carroll County records, the bridge traces its history to late 1912, when the county board of supervisors awarded a contract to build all of the county's steel and wood bridges for 1913 to the Standard Bridge Company of Omaha. The following spring the Iowa State Highway Commission prepared designs for nine separate pony trusses, ranging in span length from 35 to 75 feet. In July 1913 the county authorized construction of fifteen steel bridges built from theses designs. The ISHC's First Annual Report announced that the bridges were to be used "largely as standards for other counties desiring that type of bridge." The report concluded that the structures, "while not possessing the neat appearance or the rigidity of the slab floor type of bridge, seemed to be very much in demand by the counties having a considerable number of drainage ditches to span, which deserved cheaper construction." The list included four 50-foot pony trusses, among them this span in Pleasant Valley Township. Standard Bridge subsequently erected the bridges for the aggregate sum of $29,174. Since its completion in 1913, this bridge has carried vehicular traffic with only minor, maintenance-related repairs.

The Iowa State Legislature passed the Brockway Act on April 9, 1913, largely in response to poor road and bridge contracting practices among the counties. As one of the act's key provisions, the newly reorganized state highway commission was directed to design (or approve designs for) all vehicular bridges costing more than $2,000. ISHC, under the direction of Designing Engineer C.B. McCullough, prepared so-called "special designs" for the major crossings. For the myriad small ditch and stream crossings across the state, ISHC developed standardized plans. These standards initially included concrete slabs and culverts and steel through and pony trusses. The plans submitted to Carroll County in the spring of 1913 represented the prototypes for ISHC's pony trusses: experimental designs that soon became the basis for the ISHC X Series standards. This unimposing Carroll County span is thus technologically significant because it represents the model for the state's X-1 Standard [adapted from Fraser 1992].