Year constructed: 1913
Bridge type: Rigid-Connected Warren Pony Truss
National Register of Historic Places status: Bridge is un-evaluated in its current location
Length: 37 feet
Width: 15.8 feet
Spans: 1
FHWA: 094140
Jurisdiction: City of Carroll
Location: In Veterans Park, off of N Grant Road in Carroll, Section 18, T84N-R34W (Grant Township)
Details
This modest span is a 35-foot, rigid-connected Warren pony truss, supported by a timber substructure, located on Quail Avenue five miles southeast of Carroll. According to Carroll County records, the bridge traces its history to late 1912, when the 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 these 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 ISHC list included this 35-foot pony truss between Sections 2 and 3 of Pleasant Valley Township. Standard Bridge subsequently erected the bridges for the aggregate sum of $29,174, including $1,247 for this span. Since its completion in 1913, this bridge has carried vehicular traffic with only minor modification.
At first glance, this bridge appears to be a typical example of ISHC's standard pony truss type. What distinguishes this structure is that not only is it a typical example, it is the prototypical example. 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. McCollough, 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. The smallest of these, a 35-foot, two-panel pony truss, was finalized as the X-1 Standard with some modification on January 1, 1914. 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].