In April of 2004, the 1990 MOU was superseded by a Programmatic Agreement (PA) signed by the IDOT, IHPA and FHWA. The present PA is effective for 5 years from the date of its ratification and will be review for extension and/or modification. The PA established that:
The following items, the majority of which are derived from data contained in the Illinois Structure Information System (ISIS), are included within the HBS for each structure listed:
Except for “Group” and NRHP “Code”, the items listed for HBS structures are the same as those provided in the ISIS in accordance with direction provided by the IDOT Structure Information and Procedure Manual.
The “Group” designation for HBS structures provides information relative to “primary” (P) or “alternate” (A) status of the bridge, as well as the period of time within which the structure was built. The designation of “alternate” is a substitution for the term “secondary” used in the PA with the IHPA and FHWA for addressing historic bridge issues. Each bridge type included on the HBS is “divided” into one, two or three groups. Bridges “divided” into more than one group have each group established to include only those structures constructed within a specified time period. For example, a specific bridge type may have three groups, with the first group including all bridges constructed in 1900 or prior, the second group including all bridges constructed in 1901 through 1920, and the third group including all bridges constructed after 1920. In this example, a secondary or “alternated” structure on the HBS of a specific bridge type built in 1911 could then have a “Group” designation of “2A” on the HBS..
The “Code” designation for HBS structures provides information for the bridges that are individually listed on the NRHP; the bridges that located within a National Register Historic District (NRHD); and the bridges that are presently not old enough for inclusion on the NRHP, which are identified by “**”.
When using the ISIS to determine whether or not a structure is included on the HBS, the only indicator is ISIS Item 37 (Historical Significance Indicator). Bridges on the HBS are coded “1” through “7” for ISIS Item 37. If a bridge with historic significance is included as a “secondary”/“alternate” structure on the HBS, ISIS Item 37 will be coded either “4” or “6”. The “primary” examples on the HBS have ISIS Item 37 coded “1”, “2”, “3”, “5” or “7”. This correlation between ISIS Item 37 coding and the status of a bridge on the HBS as either a “primary” or “secondary” example is not presented in the Structure Information and Procedure (SIP) Manual. A recommendation has been made that future revisions to the SIP Manual for Item 37 include revisions that explain the correlation between the applied codes and the HBS.
To the casual observer, the designation of bridges as historic appears to be somewhat arbitrary. However, a significant amount of time, effort and interagency coordination went into the development of the HBS. A recommendation has been made that the SIP Manual be revised to include information in the appendix relative to the process used for assigning historic significance to bridges of the HBS.