In addressing historic bridges in Missouri, the term “bridges” collectively refers to both public and privately owned highway, railroad, and pedestrian bridges, viaducts, and culverts. Historic bridges are listed on or eligible for listing on the National Register of Historic Places (NRHP). MoDOT is responsible for identifying and managing historic bridges associated with highway projects.
Unlike most other types of cultural resources in Missouri, historic bridges have been inventoried and evaluated statewide. The Surface Transportation and Uniform Relocation Assistance Act of 1987 (STURAA) directed all states to inventory their historic bridges. There are about 24,000 bridges in the State (State, County, and City bridges). The 1996 Missouri Historic Bridge Inventory survey evaluated approximately 11,000 of them, which were built before 1951. Of these, 399 were considered possibly eligible, eligible, or listed on the NRHP. This list, with some modifications, became the Missouri Historic Bridge List (MHB List). It contains about 25 different types of structures including various metal pony trusses and through trusses, wooden trusses, concrete arches and rigid frames, stone arches, and so forth. All were built from 1858 to 1954.
Bridges not on the MHB List are evaluated for eligibility to the National Register of Historic Places, in consultation with the State Historic Preservation Office (SHPO). A project can have “no effect”, “no adverse effect” or an “adverse effect” on a historic bridge.
An adverse effect occurs when a project would harm a historic bridge’s ability to convey it’s historic significance. Examples of adverse effects include demolition, removal from the original location, removal or alteration of original bridge parts, and introduction of new elements that diminish the bridge’s significant historic features.
If a project will have an adverse effect on an historic bridge, efforts are made to minimize the effects through redesign of the project. If an adverse effect cannot be avoided a Memorandum of Agreement is negotiated outlining measures to mitigate the effects of the project on the resource.
Mitigation typically includes archival photographs, and preparation of a thorough history and detailed written description, which are then archived at the state or national level depending upon the range of significance. Mitigation also may include marketing and advertisement for adaptive reuse at the existing location or at a new location, dismantling and storing the bridge for future use on another site, or salvaging important historical components of the bridge for reuse as educational or interpretive materials, or reusing salvaged components on other similar historic bridges in need of rehabilitation. An article in MoDOT's Spring 2002 issue of Pathways magazine, "For a Free Bridge Call MoDOT" describes how historic bridges can be given a new function.
General information can be found at the Historic Bridges of the Midwest website and at A Context for Common Historic Bridge Types. Additional information is provided in the MoDOT brochure, Historic Bridges and Transportation Projects in Missouri. It is also available in a print version for downloading.