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California Historical Bridges and Tunnels

California has a wealth of iconic landmarks that let residents and visitors alike know they are in the Golden State. Many of these landmarks are the state's historic bridges and tunnels that range from the spectacular Bay Area and elegant Los Angeles River bridges, to the simple and aesthetic bridges of the Central and North Coast, and the rustic bridges in rural areas throughout the state.

The Caltrans Division of Environmental Analysis and cultural resources specialists in the 12 district offices work closely with Caltrans engineers and maintenance staff, as well as local governments and historic preservation groups, to preserve and protect the historic bridges and tunnels of the Golden State.

This webpage is a cooperative effort among the Division of Environmental Analysis, the Caltrans Transportation Library and History Center, and the Division of Engineering Services to provide information to Caltrans staff, other governmental entities, consultants, engineers, cultural resources specialists, and anyone who is interested in these resources. It serves as a portal to information about these resources, including historic contexts for historic bridge types, information on individual historic bridges, and technical guidance.

If you have questions or comments about historic bridges or the historic bridge inventory, please contact the Cultural Studies Office. 

Historic Bridge Inventory

The original statewide historic bridge inventory was completed in 1986. It was most recently updated in 2015 for bridges built between 1965 and 1974, and the National Register of Historic Places (National Register) status of some of the bridges has changed. The update evaluated most of the state highway and local roadway bridges constructed prior to 1974. Bridges constructed in 1975 and later are expected to be addressed under the Advisory Council on Historic Preservation's Program Comment for Streamlining Section 106 Review for Actions Affecting Post-1945 Concrete and Steel Bridges issued November 16, 2012.

Each bridge received a National Register status designation and are placed in one of the five numeric categories as follows:

  1. Listed in the National Register.
  2. Eligible for National Register listing.
  3. May be eligible for National Register listing.
  4. Unevaluated. Generally, Category 4 bridges constructed before 1965 are associated with properties that have not yet been evaluated, such as railroads, canals, or potentially eligible historic roads.)
  5. Ineligible for National Register listing.  

Historic Bridge Inventory List

Caltrans Structure Maintenance and Investigations keeps the official Historic Bridge Inventory List. Consultants working on Caltrans projects can obtain copies of current historical rating sheets needed from the Caltrans district. The public can inquire about bridge status or obtaining a copy of the list with CSO Jill Hupp at jill.hupp@dot.ca.gov.

Background

In 1984-1986, Caltrans conducted a statewide inventory of highway bridges with some potential for historic significance. Many old bridges need to be rehabilitated or replaced every year, and virtually all of these projects were federally-funded and subject to federal historic preservation laws. In the 1970s, the Federal Highway Administration (FHWA) recognized that it was inefficient to continue to evaluate each historic bridge on a case-by-case basis. It encouraged the various state highway agencies to survey bridges on a comprehensive basis.

Methodology

Caltrans' master inventory of bridges included 23,000 structures. By eliminating those that were built within the past forty years, and those that were not highway bridges per se, but culverts, railroad bridges etc., the number of bridges needing to be surveyed was substantially reduced. One thousand bridges were identified as having some potential for historic significance; these made up the survey population. A four-step survey process consisted of conducting background research on bridge building in California, gathering data on each bridge in the survey, developing a quantitative evaluation system, and evaluating each bridge according to the system.

The quantitative evaluative system was derived in large part from previous surveys in other states but adapted to meet California circumstances. Developing the system involved identifying attributes that might define significance, then assigning a weighted value to each attribute. Age, for example, is commonly taken as an indicator of potential significance; rarity is another. A very large bridge is maybe more valued over a small bridge because it is a more dramatic achievement in engineering science. Bridges are also valued when they are beautiful, designed by a famous engineer, representative of innovative technologies, important to local transportation history or other local historical trends, or when they possess unusual ornamental or structural features.

Special conditions in California were also considered, such as a high incidence of historic concrete bridges. Separate systems were developed for the major concrete bridge types (arches and girders), in addition to a system for metal truss bridges.

The final step in the inventory and evaluation process was to apply the evaluation system to the survey population. To ensure consistency, Caltrans developed guidelines for applying the criteria, which were as specific as possible, particularly with respect to the more subjective categories. When the guidelines were applied to all the bridges in the survey population, a computer database program generated lists of bridges ranked numerically.

The distribution of bridges on this list was predictably bell-shaped, with a small number of excellent bridges scoring very high, a number of bridges scoring very low, and a lump of bridges in the middle. Very low-scoring bridges were eliminated from further consideration, while very high-scoring bridges were placed into the National Register-eligible category. The middle group was reviewed by a team of evaluators, including representatives from Caltrans, FHWA, and the California Office of Historic Preservation. The review relied on the point system as well as other considerations that may not have been reflected in the numerical evaluation system.

Historic Bridge Contexts and Surveys

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As a result of the original 1980s survey and the subsequent updates, numerous historic contexts were developed and can be accessed from the links below.

Standard Environmental Reference (SER), Volume 2 - Cultural Resources

Volume 2 of the SER provides guidance for the consideration of cultural resources, including historic bridges and tunnels, as a critical part of all phases of project development, construction, permitting, right of way, and maintenance activities. Caltrans must comply with federal and state environmental laws and regulations designed to protect cultural resources significant in American archaeology, architecture, history, culture, and engineering.

The following sources describe project development, construction, permitting, right of way, and maintenance activities that may need to be considered for compliance with federal and state environmental laws and regulations for historic bridges and tunnels:

Bridge activities that do not need environmental review; that typically have no potential to affect historic properties; or that are completed in a manner consistent with the Secretary of the Interior Standards for the Treatment of Historic Properties in accordance with Caltrans 2014 First Amended Section 106 Programmatic Agreement (PDF).  Stipulation X.B.1 and upon review by Caltrans Professionally Qualified Staff (PQS) Principal Architectural Historian, will result in a no adverse effect on historic bridges or tunnels. The Caltrans Standard Environmental Reference Environmental Handbook, Volume 2, contains guidance for the situations described above in Chapters 4 and 7, Exhibit 7.3: Historic Bridges and Tunnels Screened Undertakings and Activities, and Exhibit 7.4: Historic Bridges and Tunnels No Adverse Effects with Standard Conditions.

Federal Highway Administration - Environmental Review Toolkit and Bridge Preservation

FHWA assists in the preservation of historic bridges and encourages states to incorporate the concepts of context sensitive design in the rehabilitation and reuse of historic bridges. Programs for historic bridge preservation on this site include:
  • National Historic Covered Bridge Preservation Program
  • Transportation Enhancements Program
  • Highway Bridge Replacement and Rehabilitation Program
Additional resources on this site include: FHWA Bridge Preservation Guide: Maintaining a Resilient Infrastructure to Preserve Mobility (PDF) provides bridge-related definitions and corresponding commentaries, as well as the framework for a systematic approach to a preventive maintenance program.

Bridge Preservation Toolbox provides links to the following topics:

  • Legislation and Policies
  • Research and Development
  • Bridge Management
  • Bridge Preservation Treatments

Technical Guidance

Transportation Library and History Center Historic Bridge and Tunnel Information

The Transportation Library and History Center maintains a searchable Historic Bridges database that contains data and photographs for historic bridges and tunnels listed or determined eligible for listing in the National Register. Data include structure number, location, summary description, structure type, distinctive features, and other data to assist with understanding significance. Additional information is available in the historic bridge files of the Transportation Library and History Center.

Transportation Library and History Center
1120 N Street, Room 1430
Sacramento, CA 95814
Hours: 9:00-4:00, Monday - Thursday 
Phone: 916-654-4601 
Email: library@dot.ca.gov

Other Information on Caltrans Bridges