Time is taking its toll on many Oklahoma highway bridges. These aging structures, some built more than seventy-five years ago, are wearing out, while others have become functionally obsolete or dangerous under the speed and weight of modern traffic. Yet viewed from another perspective, the old bridges are valuable examples of the industrial and engineering achievements of the past and evidence of how transportation gave shape and vitality to our communities. Out of these concerns, that at times unfortunately pit the interests of history against the practical needs of today, came the origins of the present study.
Further impetus came from federal legislation. Congress acknowledged in 1987 that historic bridges were "important links to our past" and urged that plans be made to study, reuse, and preserve the most worthy examples of bridge building in the states. Having what it believed were approximately 1,800 bridges with potential historical value on its streets and roads, Oklahoma initiated this project to survey, research, and assess these spans. Fundamental information about the state's early bridges would be gathered by survey, subsequently making it possible to:
- evaluate individual bridges in relation to the overall transportation history of the state,
- determine the number and condition of bridges by type and permit appropriate comparisons to be made,
- focus on those structures which may be worthy for inclusion on the National Register of Historic Places (NRHP) and develop plans for their management, and
- remove from further consideration those bridges that do not meet the requirements for eligibility to the National Register.
The project confined the study to structures over 20 feet in span and built prior to 1955. Adopting a 1955 cutoff date, rather than the more typical 50 years old standard of the NRHP, gives greater longevity to the project before revisions become necessary. Under an agreement between the Oklahoma Department of Transportation (ODOT) and the Oklahoma State Historic Preservation Office (SHPO), the project was limited to evaluating structures in the following eight general categories.
Steel Through Trusses
Steel Pony Trusses
Steel Deck Trusses
Concrete Deck Arches
Concrete Through Arches
The core list of bridges for the survey and inventory came from the computer files of ODOT in Oklahoma City. However, the number of bridges involved continually fluctuated as the project progressed, a condition explained by several factors. They included bridges incorrectly identified as to type, spans
that had recently been replaced or destroyed, and those previously cleared for removal after review by the SHPO, all of which resulted in moderately shrinking the pool of subject bridges. Case-by-case clearance procedures also accounted for changes. The final list of 1,555 structures reflects these changes and also includes several bridges discovered in the course of fieldwork; the latter structures ordinarily had no ODOT identification number. The survey found no examples of suspension bridges or steel arches.
The field research and photo-documentation produced an extensive database that supported the project through several stages of development. It was confirmed by the survey that the overwhelming majority of historical bridges are steel truss spans. Although virtually all of them qualify as standard in type and design, they demonstrate the many advantages of this kind of structure and why it achieved such widespread popularity in Oklahoma and throughout the United States. Likewise, these trusses in the state exemplify the technology of bridge building during the first one-third of this century and they exhibit the quality and durability of mass manufactured bridges built by a cross section of national and regional companies. Steel trusses made up approximately 92% of the bridges in the survey, and roughly 73% of the total consisted of pony trusses. Judging from surviving examples (564), the workhorse structure in Oklahoma was the Warren pony truss, typically strengthened by additional vertical members, that accounted for 36% of the inventory. Based on project research and data supplied by ODOT, all bridges in the survey were constructed after 1900, with the single exception of an 1896 through truss in Seminole County that had once been a railroad span.
The process of determining which bridges have the highest degree of merit or importance began with establishing the inventory and moving through several phases of research and review. The purpose was to identify those features, whether of an engineering or historical nature, that would contribute to a structure's significance. Date of construction, bridge type and size, apparent structural integrity, builder, and location were elements in this documentation that made possible preliminary assessments. Seeking similar kinds of information about Oklahoma's early bridges gave direction to the research as well. Since great importance was placed on finding reliable sources of historical information, the project proceeded along several lines, going beyond the computerized files, maps, bridge plans, and printed records of the state highway commission, all of which are kept by ODOT. A broad scope of research covered major national engineering journals and popular magazines published in the state and region. Research also extended from archival collections in state and university centers to documents located in county courthouses and local libraries. What was learned from these varied sources of information helped to define the patterns of development in Oklahoma and to establish a historical context by which individual bridges were evaluated for their significance.
In assessing Oklahoma bridges for their cultural and technical value, the process adhered to the standards set by the National Register of Historic Places. Consideration was also given to the guidelines followed by such professional organizations as the American Society of Civil Engineers for recognizing technology with important historical significance. Older bridges received careful consideration since Oklahoma's bridges date almost exclusively from the twentieth century. The evaluation similarly weighed more heavily the major bridges because they generally represented greater effort and resources invested by the community. Being able to document the details of their construction, including date, builder, and location, makes some early bridges more credible historical assets and strengthens their case in relationship to others of the same type. The overall review process took into account the particular circumstances of history in Oklahoma that resulted in a unique mix of bridge types that, when combined with the number and quality of surviving examples, determines the frame of reference for choosing structures with outstanding characteristics. By taking this approach, the evaluation selected as historically valuable those structures which most effectively tell the story of bridge building and highway development in Oklahoma.1
NOTE Oklahoma bridges are identified at places in the text by a series of numbers and letters. ODOT assigns these codes based on map coordinates which locate the bridges on the road system. The first two digits identify the county. For example, the number "20" denotes Custer County. Since the structure numbers are geographical points, they can change as roads are remeasured, and a relocated bridge would likewise acquire a new number at a different site. Because the numbers are unwieldy and subject to revision, they have been used sparingly in the text.