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 Janice Calpo in the Caltrans Division of Environmental Analysis at (916) 653-0802.
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:
- Listed in the National Register.
- Eligible for National Register listing.
- May be eligible for National Register listing.
- 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.)
- Ineligible for National Register listing.
- Historical Significance - State Bridges [pending]
- Historical Significance - Local Agency Bridges, March 2019 (PDF - 18 MB)
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.
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.
- Caltrans Statewide Historic Bridge Inventory: 2015 Update (PDF) (Caltrans 2015) (Caution: large PDF file, 81 MB)
- Caltrans Statewide Historic Bridge Inventory: 2010 Update (PDF) (Mead Hunt, Inc. 2010)
- Caltrans Statewide Historic Bridge Inventory Update: Tunnels (PDF) (Myra L. Frank Associates, Inc. 2006)
- Caltrans Statewide Historic Bridge Inventory Update: Bridges that were not individually surveyed and evaluated (PDF) (Caltrans 2005)
- Caltrans Statewide Historic Bridge Inventory Update: Timber Truss, Concrete Truss, and Suspension Bridges (PDF) (JRP Historical Consulting 2004)
- Caltrans Statewide Historic Bridge Inventory Update: Metal Truss, Movable, and Steel Arch Bridges (PDF) (JRP Historical Consulting 2004)
- Caltrans Statewide Historic Bridge Inventory Update: Concrete Box Girder Bridges (PDF) (Myra L. Frank & Associates, Inc. 2004)
- Caltrans Statewide Historic Bridge Inventory Update: Concrete Arch Bridges (PDF) (JRP Historical Consulting 2004)
- Caltrans Statewide Historic Bridge Inventory Update: Survey and Evaluation of Common Bridge Types (PDF) (Caltrans 2004)
- City of Los Angeles Monumental Bridges 1900-1950, Historic Context and Evaluation Guidelines (PDF) (JRP Historical Consulting 2004)
- Survey and Evaluation of Masonry Arch Bridges (PDF) (Caltrans 2003)
- Historic Context Statement, Roadway Bridges of California: 1936-1959 (PDF) (JRP Historical Consulting Services 2003)
- Historic Truss Bridges in California Thematic Determination of Eligibility (PDF) (Caltrans 1985)
- Historic Bridges in California: Concrete Arch, Concrete Girder, Concrete Slab, Canticrete, Stone, Masonry, Suspension, Steel Girder and Steel Arch (Thematic) – Determination of Eligibility (PDF) (Caltrans, 1986)
- Historic Highway Bridges of California (Caltrans 1990). Copies of this publication are limited. Contact the Division of Environmental Analysis for a copy.
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:
- Highway Design Manual
- Bridge Memo to Designers
- Maintenance Manual
- Construction Manual
- Technical Manuals
- Project Development Procedures Manual
- Local Assistance Procedures Manual
Federal Highway Administration - Environmental Review Toolkit and Bridge Preservation
- National Historic Covered Bridge Preservation Program
- Transportation Enhancements Program
- Highway Bridge Replacement and Rehabilitation Program
- Historic Bridges, Communities of Practice - Hosted by the American Association of State Highway and Transportation Officials (AASHTO) Center for Environmental Excellence and includes case studies, references, and a forum for participants to identify emerging issues, trends, procedures, research, and data needs associated with the identification, evaluation, and management of our nation's historic bridges.
- A Context for Common Historic Bridge Types (PDF) (10.6 MB) - National Cooperative Highway Research Program's NCHRP 25-25, Task 15, October 2005 provides the historic context for 50 of the most common historic bridge types in the United States.
- Guidelines for Historic Bridge Rehabilitation and Replacement (PDF) originally developed under the NCHRP and adopted as an AASHTO publication, presents the state of the practice and guidance for making decisions for historic bridge rehabilitation.
- Case Studies on Rehabilitation of Historic Bridges (PDF) - AASHTO Historic Bridges Communities of Practice provides guidance on making decisions whether to rehabilitate historic bridges through a compilation of 16 "real world" rehabilitation case studies on a variety of historic bridge types.
- AASHTO Center for Environmental Excellence includes information, resources, and best practices for a variety of historic preservation and cultural resource areas, including historic bridges and historic bridge inventories in other states.
- Best Practices for the Rehabilitation and Moving of Historic Metal Truss Bridge (PDF) available from the Virginia Transportation Research Council and describes "the process followed for the recent rehabilitation of a historic truss in Goshen, Virginia, and discusses the issues faced by those moving and rehabilitating historic metal truss bridges."
- Best Practices and Lessons Learned on the Preservation and Rehabilitation of Historic Bridges (PDF) was developed under a NCHRP "rapid research" project on behalf of the AASHTO Standing Committee on the Environment. This publication has not been adopted by AASHTO but provides national case studies of preservation practices for historic bridges.
Bridge Preservation Toolbox provides links to the following topics:
- Legislation and Policies
- Research and Development
- Bridge Management
- Bridge Preservation Treatments
- List of Common Bridge Design Terms and Definitions - The Center for Environmental Excellence Historic Bridges Community of Practice forum provides an online glossary of common bridge design terms and definitions.
- Secretary of the Interior's Standards for the Treatment of Historic Properties - These standards are federal regulations that provide an explanation of the four treatment approaches: preservation, rehabilitation, restoration, and reconstruction.
- Differences between cultural resources specialists and engineers in the technical vocabulary when referring to design treatments for historic bridges (PDF) - Preservation professionals and bridge engineers use a different technical vocabulary when referring to design treatments for historic bridges, which results in differences in perspectives. Understanding the differences in technical vocabulary is vital to effective communication and collaboration on historic bridge projects. This document highlights the different perspectives on bridge activities based on the definitions of preservation, rehabilitation, restoration, and reconstruction in the Standards and the perspective of bridge engineers.
- A Management Plan for Historic Bridges in Virginia (PDF) - The Virginia Transportation Research Council adapted the Secretary of the Interior's Standards for the Treatment of Historic Properties for application to historic bridges. The standards have been interpreted and applied overwhelmingly to one type of historic resource (i.e., buildings). A Management Plan for Historic Bridges in Virginia addresses the unique requirements of historic bridges and identifies specific instances of the application of the Secretary of the Interior's Standards for the Treatment of Historic Properties to historic bridges.
- National Park Service Preservation Brief 15: Preservation of Historic Concrete - This document provides guidance on appropriate cleaning methods for concrete on historic structures, including bridges and tunnels.
- National Park Service Preservation Brief 1: Assessing Cleaning and Water-Repellent Treatments for Historic Masonry Buildings - This document provides guidance on cleaning historic masonry structures.
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
Other Information on Caltrans Bridges
- California Toll Bridge Directory
- The Toll Bridge Program - provides histories and facts about Caltrans toll bridges.
- For Caltrans bridge technical specialists and bridge design engineers, see Offices of Structure Design.
- Structure Maintenance & Investigations Bridge Links
- Local Highway Bridge Program