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Last Updated: Friday, February 3, 2012 11:30 AM

Exhibit 7.5: Bridge Numbering and Historic Status Codes

Exhibit 7.5 PDF version here.

Bridge Numbering System

State-owned bridges are listed in the Caltrans historic bridge inventory in numerical order, according to the following hierarchy: by district, in numerical order; by county number, in numerical order within the district; and by bridge number. Bridges owned by local agencies follow a similar numerical pattern but are listed first by county, then bridge number. In addition, local bridges include the letter “C” in the county number. For instance, Bridge #51-10, is located on Route 101 crossing Zaca Creek in Santa Barbara County. It is listed under District 5, under County 51 (Santa Barbara), and under number 51-10. Bridge #51C-47, is a local bridge in Santa Barbara County that crosses San Ysidro Creek and carries San Leandro Lane.

For purposes of assigning bridge numbers, Caltrans adopted a system in which all the counties in California were numbered sequentially by geography, starting with the northwest corner of the state and proceeding eastward, then moving to the next “row” of counties. Bridges are arranged by bridge number rather than by route and post mile.

In addition to the bridge number, the inventory list a county-route-post mile location, a common name for the bridge, the name of the municipality (if any) in which the bridge is located, and a “historical significance” category.

To determine the Bridge Inventory’s National Register status for a bridge as described above, locate the bridge by its bridge number and identify its “historical significance” category.

California Historic Bridge Inventory Historic Status Codes

The Structures Maintenance, Division of Structures database for state bridges and local bridges contains National Register of Historic Places (National Register) significance ratings. The “Historical Significance” classifications correspond to the Caltrans “National Register status” categories for each bridge. In some cases these categories do not correspond to the Office of Historic Preservation’s Historical Resources Status Codes (OHP status code), which are provided in parentheses. The significance categories are defined as follows:

Category 1. Listed in the National Register

A small number of bridges fall under this category. Either of the following documents may serve as the Bridge Evaluation for a Category 1 bridge (OHP status code 1S or 1D):

  1. A copy of the Historic Bridge Inventory “Bridge Rating Sheet” for that bridge, available in the District or upon request from CCSO; or
  2. A copy of the National Register nomination form for the bridge, usually available from the Office of Historic Preservation.

Category 2. Determined Eligible for the National Register

Most Category 2 bridges were determined eligible as a result of the California Historic Bridge Inventory and subsequent evaluations and updates since 1986. Either of the following documents may serve as the Bridge Evaluation for a Category 2 bridge (OHP status code 2S or 2D, and/or for state-only projects for state-owned bridges 4CM):

  1. A copy of the Historic Bridge Inventory “Bridge Rating Sheet” for that bridge, available in the District or upon request from CCSO; or
  2. Copy of the SHPO letter concurring with the determination or the Keeper of the National Register’s letter documenting the Keeper’s determination.

Category 3. Appears Eligible for the National Register, but not Officially Determined Eligible

Most of the bridges previously identified as Category 3 were evaluated in the 2006 update to the Historic Bridge Inventory and were changed to Category 2, 4, or 5 based on the results of the survey. Seven bridges identified as Category 3 (OHP status code 3S or 3D) structures in the original 1986 survey were evaluated in the updated survey. These are structures that are owned by federal or other state agencies. They will retain their Category 3 designation and will require re-evaluation if located within the APE for a project.

Category 4. Status Undetermined, Requires Further Research

Category 4 (OHP status code 7N, 7N1 or 7R) is a default category used for bridges not evaluated as part of the Historic Bridge Inventory. Under the updated survey, it primarily will include bridges that are not individually significant under any of the National Register criteria, but may be contributors to a larger property, such as bridges constructed by the Bureau of Reclamation as part of the Central Valley Project canals and bridges on old Route 66 in San Bernardino County. Many railroad bridges also will be included in this group. If a Category 4 bridge is located within the APE for a project, an evaluation will be needed to determine whether the bridge is a contributor to a larger historic property (OHP status codes may vary depending on the outcome of the evaluation).

Category 5. Not Eligible for Listing in the National Register

Category 5 bridges were determined not eligible through the Section 106 process, either through a consensus determination with SHPO or a formal determination of ineligibility by the Keeper of the National Register. The vast majority of bridges fall into this category. A copy of the relevant Historic Bridge Inventory printout sheet serves as the evaluation for a Category 5 bridge in most cases. All bridges constructed before 1960 have been evaluated in the Bridge Inventory Update completed in 2006. Bridges constructed in 1960 or later must be evaluated if they will become 50 years old by the time a project would be completed.