With the passage of the Surface Transportation Assistance Act of 1978, efforts to identify bridges with historic significance were renewed. In December 1980, based on review of available databases, 700 Illinois bridges were identified as having the potential for historic designation. A committee was formed within the IDOT to perform further review; to assist in the categorization of bridges; and to develop of criteria for determining historic significance.
In July 1981, the committee issued draft guidelines for the identification and categorization of bridges with historic significance. At that time, 241 bridges were identified by the committee as having the potential to be designated historic, and the actual preservation of 118 of these bridges was thought to be sufficient to physically establish a historic record of bridge construction.
In May 1983, internal review of the committee recommendations had been completed and additional scrutiny the Illinois bridge inventory had been conducted. The number of bridges with the potential for historic designation was then determined to be 398. These structures were divided into 25 bridge types. Of these bridges, IDOT identified 120 bridges that would “illustrate the advancement of structural engineering in bridge design” in Illinois. A list of the 120 bridges was distributed to all the IDOT Districts and field data was obtained for each structure.
After the establishment of the tentative list of historic bridges in 1983, discussions with the FHWA and the Illinois Historic Preservation Agency (IHPA) began. In November 1990, with the signing of a Memorandum of Understanding (MOU), compliance procedures were established between the IDOT, IHPA and FHWA. The MOU required the establishment of a list of structures with historic significance to be called the Historic Bridge Survey (HBS). Some 350 bridges were included in the initial HBS, and these structures were to be divided then into “primary” and “secondary” examples of the various bridge types.
UPDATE 1/12/12: The Historical Bridge list and the Programmatic Agreement are currently being updated.