HISTORIC HIGHWAY BRIDGES OF OREGON

Horsetail Falls Bridge (1914), old Columbia River Highway, Oneonta vicinity, Multnomah County

NEED

The primary responsibility of the Department of Transportation is to provide a safe, efficient transportation system. To finance improvements to that system, state and local funds are matched with federal funds administered by the Federal Highway Administration, United States Department of Transportation. Transportation projects using federal matching funds or requiring federal permits must be developed in accordance with the appropriate federal laws and regulations. One such body of federal law relates to historic resources and ensures that these resources are fully considered in transportation planning. The department initiated this historic highway bridges study to assist in fulfilling federal requirements on historic preservation.

The federal laws on historic preservation sometimes conflict with the department's primary responsibility. Such conflicts are not easily resolved, particularly in the case of bridge rehabilitation or replacement projects. This study, by identifying those bridges which are of historic significance, helps the department comply with the historic preservation laws. As a result, the department can better plan and schedule bridge rehabilitation and replacement projects.

In 1966, the United States Congress enacted the National Historic Preservation Act, which strengthened the federal commitment to preserving significant historic resources. While there had long been an effort to preserve historic properties of national importance, this act extended protection to historic resources with state and local significance as well.

The National Historic Preservation Act of 1966 authorized the Secretary of the Interior to develop and maintain the National Register of Historic Places. (The National Register had been created by law in 1935, but was expanded under the authority of the 1966 Act.) The National Register is the official list of districts, sites, buildings, structures, and objects significant in American history, architecture, archeology, and culture. Furthermore, the Act established the criteria for resources to be eligible for listing on the National Register (Figure 15). The National Register currently includes about 37,500 properties and districts, of which over 500 are in Oregon.

FIGURE 15. Evaluation criteria for inclusion in the National Register of Historic Places [Source: Section 101(a)(1)(A), National Historic Preservation Act of 1966, as amended, and 36 CFR Part 60.6.]

The National Historic Preservation Act of 1966 also created the Advisory Council on Historic Preservation and authorized the Council to assist in protecting National Register properties from unnecessary adverse effects due to federally funded or licensed projects (e.g., bridge replacements). Section 106 of the Act requires that projects affecting historic resources be coordinated with the Advisory Council and that the Council be given a reasonable opportunity to comment. This Act also requires that the State Historic Preservation Office be consulted and invited to comment on federally-assisted projects.

An important supplement to the 1966 Act was Executive Order 11593, issued in 1971. Previously, the law provided protection only to historic properties listed on the National Register. The Executive Order extended that same protection to all historic properties considered eligible for the National Register, regardless of whether they were listed or under consideration for listing. This order required the state to evaluate all buildings, structures, or sites potentially affected by federal projects and determine whether they are eligible for inclusion on the National Register according to the Act's criteria. If an eligible property is affected by a project, the final judgment on its eligibility is made by the Keeper of the National Register, National Park Service, United States Department of the Interior, Washington, D.C.

National Register-eligible historic properties are also afforded protection from federal projects by Section 4(f) of the Department of Transportation Act of 1966. This law states, in part, that no project can be approved for federal transportation funding that requires the use of a significant historic resource, unless there is no feasible and prudent alternative and all mitigation options have been incorporated.

Other federal or state regulations and rules to be considered include the National Environmental Protection Act (1969), the Council on Environmental Quality guidelines, the ODOT Action Plan, and Oregon's Statewide Planning Goals.

As a result of this body of legislation, historic preservation has assumed importance in highway planning. In recent years, the department has planned for the replacement or rehabilitation of a large number of bridges and has had to evaluate the historic significance of the bridges on a case-by-case basis. Comprehensive historic information about Oregon's bridge population was not available for comparative purposes. Historic judgments about bridges were difficult to make at best without knowing the characteristics of the total population of Oregon's older bridges.

PURPOSE

The purpose of the historic bridges study was to inventory, evaluate, and assess the state, county, and local highway bridges in Oregon to determine which structures were National Register eligible.

Specifically, the study serves to make bridge project development more efficient and fulfill federal laws and regulations, as follows:

1. Identifies those highway bridges which are historically significant and meet the National Register eligibility criteria.

2. Conversely, identifies bridges that are not eligible for the National Register and facilitates the replacement planning process.

3. Allows the identification of bridge replacement projects involving National Register eligible structures early in project development, thus providing time to complete the necessary actions mandated by law.

4. Eliminates the need to conduct historic research on each bridge on a case-by-case basis.

5. Provides the comparative data to develop appropriate mitigation for historic bridges proposed for replacement.

6. Provides information for the development of a preservation priority plan.

METHODOLOGY

Basic Parameters

The Department of Transportation maintains a computerized listing of most highway bridges in state, county, and local ownerships in Oregon. This file includes about 7,000 structures and contains basic information invaluable for this study—bridge names, locations, types, dimensions, ownerships, and construction dates. This list imposed some basic parameters on the historic bridges study. A bridge was defined, thus:

A structure including supports erected over a depression or an obstruction, as water, highway, or railway, and having a track or passageway for carrying traffic or other moving loads, and having an opening measured along the center of the roadway of more than 20 feet.

In accordance with the definition of a bridge, structures less than 20 feet were excluded from the study. Only structures of sufficient size to have involved substantial engineering were examined.

The study population consisted of highway bridges regularly inspected and potentially eligible for federal rehabilitation or replacement funding. The study did not normally include privately-owned bridges, such as railroad bridges, nor publicly owned bridges under the jurisdictions of federal and state agencies other than the Department of Transportation. Most all local government-owned highway bridges were included. Bridges built exclusively for pedestrian use or other non-highway uses are generally excluded, except for some railroad crossings. In the course of field inspection, many of these excluded bridges were incidentally photographed and inspected, but only for comparative purposes. Other highway structures, such as tunnels, culverts, and retaining walls, were not inventoried in the study, but may be examined in future studies.

Historic resources must be at least fifty years old, as a general rule, or be of exceptional significance or value to be eligible for the National Register. The cutoff date for the construction of the bridges in this study was set at 1941, which included some bridges a few years younger than 50 years. The cutoff date was set to include Depression-era structures approaching 50 years of age. Additionally, World War II slowed domestic bridge construction, and the post-war period saw major changes in bridge building. This cutoff date enabled the study to be current for several more years and to facilitate long-range planning decisions. Application of the pre-1941 age cutoff resulted in a study population of about 1,200 highway bridges to be screened and evaluated. Several notable post-1940 bridges were also examined, but most bridges of this age group were not inventoried.

Seventy-seven highway bridges had already been determined eligible for or listed on the National Register, mostly covered bridges and structures on the old Columbia River Highway. Since their historic status was already established, these bridges did not require a full examination but were incorporated into the study.

Field Inspection and Historic Research

Field inspection and historic research were integral to the study. Field inspection verified known information and generated new data. The study team photographed each bridge and gathered important information from the nameplates, architectural and engineering details, truss configurations (where appropriate), and the setting. Bridge logs, plans, drawings, bridge maintenance records, general project files, the Oregon State Highway Commission's biennial reports, books on bridge building, professional magazines, newspapers, and historical journals provided historic information, which was supplemented with interviews with county and city public works officials.

About 500 bridges, including all of the pre-1941 truss, arch, suspension, and moveable bridges, were field inspected. Not all of the slab, beam, and girder bridges, which account for about 80 percent of the pre-1941 constructed bridges, were field checked because they were seldom historically significant. The bridges of this type were examined by random and representative sampling. A random sample of 20 percent of the slab, beam, and girder bridges was drawn, as well as these representative groups: all of the pre-1921 bridges and all the bridges in Salem, Portland, and on the Oregon Coast Highway. Instead of field inspections, some slab, beam, and girder bridges were inventoried only by an examination of the drawings and plans. These samples of the slab, beam, and girder bridges were considered adequate to isolate the historically significant bridges and to test for potential statistical occurrence in this bridge group. Including about 150 plans inventories on the slab, beam, and girder bridges, a total of about 650 bridges, or one-half of the pre-1941 bridges, were inventoried for the study. A complete list of the bridges inventoried for the study is in Appendix G.

EVALUATION AND IDENTIFICATION

Preliminary Historic Evaluation

After the field inspection and historic research stage of the study, the bridges were preliminarily evaluated for historic significance and placed in one of three categories:

This preliminary evaluation resulted in 141 bridges being placed in categories I and II. The remainder of the bridges were Category III. Category I and II bridges were subjected to additional research and final evaluation.

Evaluation Rating System

The study team developed an evaluation system in consultation with the State Historic Preservation Office to identify the Oregon highway bridges considered National Register eligible. Various bridge evaluation systems developed by other states were reviewed, as well as systems used for other historic resources.

The evaluation rating system for Oregon's historic highway bridges is based on the National Register criteria with some minor modifications. To address a broad diversity of cultural resources, the National Register criteria, by necessity, are general in nature. Consequently, the criteria were tailored for specific application to bridges as a particular class of historic resources.

The evaluation rating system consisted principally of three measures of resource integrity and ten measures of historic significance, modeled after National Register criteria. (See Figure 15 for the National Register criteria.) Each measure contained a six-increment scale: unknown, none, low, moderate, high, and exceptional.

Measures of Integrity

To be eligible for the National Register, historic properties must possess integrity of location, design, setting, materials, workmanship, feeling and association. Three measures of integrity were developed to correspond to the National Register criteria on integrity. (The present structural adequacy or capacity of the bridge was not considered an integrity measure.)

Measures of Historic Significance

The historic significance rating system included ten measures. Measures 1, 6, 7, 9, and 10 were specific elements of the National Register criteria and reflected that wording and meaning. Measures 2 through 5 were modifications of the National Register criterion "embody the distinctive characteristics of a type, period, or method of construction." Measure 8 related to the artistic values of National Register criteria and was an attempt to measure the relationship of the bridge to the overall aesthetics of the environment.

Measure 1.	Historic Events and Persons. This measure evaluates the bridge's association with broad patterns in Oregon's history and with famous people, exclusive of the bridge designer and names of a commemorative nature. These ratings tended to be in the none to moderate range, and when applied, were usually limited to bridges at significant crossings (Willamette River in Portland), part of a major new highway development (Oregon Coast Highway) or the Depression-era Oregon Coast Bridges project.
Measure 2.	Construction Date. This measure rates how early the bridge was constructed in relation to Oregon's population of remaining highway bridges. Relocated truss bridges were rated on their original date of construction, not when moved to their present location. The scoring for the measure was as follows: Built Prior to 1910 — Exceptional 1910 - 1919 — High 1920 - 1929 — Moderate 1930 - 1940 — Low Post-1940 — None
Measure 3.	Distinctive and Important Type. This measure rates the singularity and distinctive quality of the bridge. A judgment on the importance of the general and specific type of bridge was included in this measure. This measure rated the bridges as being representative of a category.
Measure 4.	Rarity and Uniqueness of Type. This measure is similar to Measure 3, but basically indicates the number of bridges of each type. It also considers features and technologies, and whether they are obsolete (Figure 16). The rating for this measure included checking statistics on the bridges in the study to determine numbers represented in each type. (See Appendix D.)
Timber truss joint on a covered bridge (detail). Pin connection on a steel truss (detail). FIGURE 16. One of the historic evaluation criteria was rarity and uniqueness. The use of obsolete and rare technologies contributes to the historic significance of bridges.
Measure 5.	Engineering Innovation and Site Challenge. This measure rates two interdependent bridge features: engineering innovations and whether the bridge was a prototype for later bridges. Certain crossings, because of width, configuration of the stream or banks, navigational needs, or sub-surface conditions, posed difficult challenges for bridge building. This measure rates such difficulties and the quality of the engineering solution (Figure 17).
FIGURE 17. Site challenge is one of the criteria considered in the selection of the historic bridges. The Chasm Bridge (1937) is located on the near-vertical face of Neahkahnie Mountain in Tillamook County, high above the ocean on the Oregon Coast Highway.
Measure 6.	Designer and Builder. This measure ranks the importance of the bridge designer and builder and the importance of the bridge as it relates to the other works of that designer and builder. When the designer of the bridge was unknown and the bridge was credited to a bridge-building company, the rating was moderate or low based on the amount of information available on the particular company. (See Appendix B for significant bridge designers and bridge contractors in Oregon.)
Measure 7.	Artistic Values. This rating measure is a judgment of the appearance of the bridge. This and the following measure tend toward subjective judgments. Two artistic points-of-view were considered: was there a conscious attempt to beautify the design with the addition of architectural embellishments (Figure 18), and; although unadorned, is the bridge's appearance handsome in its arrangement of functioning parts?
FIGURE 18. These examples illustrate the artistic embellishments on early highway bridges. The deliberate attempts to beautify bridges add interest to the structures.
Measure 8.	Environmental Aesthetics. This measure examines how the bridge relates to its environment and the overall aesthetics of its location. It addresses questions of scale, definition, proportion, and how well the structure complements the nearby natural and cultural landscape (Figure 19).
FIGURE 19. Bridges relate aesthetically to the landscape. The pastoral setting of the Rhea Creek Bridge (1909) near Ruggs in Morrow County increases its appeal and significance.
Measure 9.	Related Historic Properties and Groupings. This measure is the National Register criterion that a property "...may be part of a group of properties that represent a significant and distinguishable entity whose components may lack individual distinction." Bridges in proximity to and historically related to other bridges or those bridges clearly part of a distinguishable and important thematic group were rated higher. Important thematic groups identified included the Willamette River bridges of Portland, Oregon's covered bridges, the reinforced concrete arch bridges of Conde B. McCullough, and the Oregon Coast Bridges project.
Measure 10.	Potential for Yielding Prehistoric or Historic Information. This measure, one of the National Register criteria, usually relates to archeological properties. Its application to Oregon's bridges was rare.

Final Evaluation

The final identification of the National Register-eligible highway bridges was based on the evaluations of a professional review team. This team consisted of volunteer bridge experts from private companies and personnel from the State Historic Preservation Office and Oregon Department of Transportation. The team members were the following:

Lewis L. McArthur, Vice President, Ray Becker Company, Portland

Louis F. Pierce, President and Chief Engineer, OBEC Consulting Engineers, Eugene

Thomas J. McClellan, Professor Emeritus, Oregon State University Engineering Department, now a consultant with CH2M-Hill, Corvallis

David W. Powers, III, Deputy State Historic Preservation Officer, State Historic Preservation Office, Salem

Walter J. Hart, State Bridge Engineer, ODOT, Salem

Jack L. Davis, Manager, Special Studies, Bridge Section, ODOT, Salem

Pieter T. Dykman, Research Coordinator, Environmental Section, ODOT, Salem

James B. Norman, Historic Bridges Study Research Associate, Environmental Section, ODOT, Salem

Dwight A. Smith, Cultural Resources Specialist and Historic Bridges Study Manager, Environmental Section, ODOT, Salem

Formal evaluation by the review team identified 68 bridges as historically significant and National Register eligible. Fifty-three other bridges were identified as having some historic interest, though ineligible for the National Register. These ineligible bridges were delegated to a reserve category (Appendix E). Several notable bridges constructed after 1940 were also reviewed by the team, but were found to be ineligible for the National Register (Appendix F). The reserve and notable post-1940 bridges will be reevaluated as the study is periodically updated. Some of the bridges may become eligible in future years as National Register bridges are lost or modified and as the bridges age.

COORDINATION AND DETERMINATION OF ELIGIBILITY

The historic bridges study was developed in cooperation and consultation with the State Historic Preservation Office. In addition to participating in the design of the study, the SHPO reviewed the evaluation rating system, served on the professional review team, and reviewed draft versions of the study report. By letter on January 10, 1985, the SHPO concurred with the final list of bridges determined National Register eligible.

The owners of the eligible bridges identified in the study, including appropriate city and county public works departments, were notified of the findings of the study and the effects on federally-funded bridge replacement projects. In January 1985, the Oregon Transportation Commission approved the study report, and the study findings were released to the public.

A thematic group request for a determination of eligibility on the 68 study-identified bridges was prepared and forwarded to the Keeper of the National Register in April 1985. In May 1985, the Keeper of the National Register determined that 57 of the study-identified bridges were eligible for the National Register. (Two of the bridges in the thematic group had previously been determined eligible by the Keeper's Office—Pass Creek Covered Bridge and the Umatilla River Bridge on S.W. 10th Street.) The Keeper took no action on the remaining nine bridges in the group, structures constructed or modified less than 50 years ago, and requested supporting information that these bridges were of exceptional significance. After receiving supplemental information on the remaining nine bridges, the Keeper of the National Register determined the remaining nine bridges National Register eligible in September 1985, completing the action on the request for a determination of eligibility.

This study report is being distributed to appropriate public agencies, historic preservation organizations, libraries, and concerned citizens for their reference and information.

The study data are valid as of July 1984. In preparation for printing, additions and modifications were made, but no exhaustive attempt was made to recheck the status of all bridges.