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Identifying and Preserving
Historic Bridges

National Register of Historic Places Evaluation Criteria

The criteria for determining eligibility for listing a bridge on the NRHP are very specific and are outlined in 36 CFR 60.4. Forest Service responsibilities for historic bridges are the same whether a bridge is listed on the NRHP or is only determined to be eligible for listing. The agency heritage resource specialist in consultation with the respective SHPO makes the determination of eligibility for NRHP listing. If the agency and the SHPO agree, the bridge is determined eligible with a “consensus determination of eligibility.” If, on the other hand, the agency and the SHPO disagree, the Keeper of the NRHP, in Washington DC, makes the final decision. The Federal agency and the SHPO usually reach an agreement on NRHP listing eligibility.

Generally, for bridges to be eligible for the NRHP, they must be at least 50 years old, be historically significant, and have a high degree of integrity. A property has a high level of integrity if it possesses characteristics that convey its historical significance through its setting, materials, design, location, workmanship, feeling, and association (see the glossary for definitions). Determining integrity will be discussed in more detail later in this section. A property’s significance in American history, architecture, archeology, engineering, and culture is determined by the integrity of the districts, sites, buildings, structures, and objects that are part of the property and its surroundings. To be considered historically significant, a bridge must meet at least one of the following basic criteria:

A. The property must be associated with events that have made a significant contribution to the broad patterns of our history.

B. The property must be associated with the lives of persons significant in our past.

C. The property must embody the distinctive characteristics of a type, period, or method of construction, represent the work of a master, possess high artistic values, or represent a significant and distinguishable entity whose components may lack individual distinction.

D. The property must show, or may be likely to yield, information important to history or prehistory.

Bridges are most often eligible for the NRHP under criterion A or C. On rare occasions a bridge may also be eligible under criterion B if the bridge builder or designer is, or was, a significant individual who had a direct role in the design and construction of the bridge. John Roebling, developer of modern cable suspension bridge technology and the designer of the Brooklyn Bridge, would be such an individual. Bridges that John Roebling designed, and whose construction he supervised, would be eligible under criterion B.

Although the NRHP is a "national" register, historic properties can be eligible because of local, State, or National significance under any of the four criteria. Under criterion A, the applicable history could be local, statewide, or National. Under criterion B, the person could be a local, State, or National figure. Under criterion C, the architectural significance could be local, statewide, or National.

Bridges may be historically significant (eligible for NRHP listing) either individually or as a contributing element to a much larger historic district. Bridges on U.S. Route 66 in New Mexico, Arizona, and California are significant as part of the Route 66 Historic Corridor District.

Not only must a bridge meet one or more of the NRHP criteria, it must have a high degree of integrity. A property has a high level of integrity if it possesses characteristics that convey its historical significance through its setting, materials, design, location, workmanship, feeling, and association. The bridge must retain, to a significant degree, at least five of the following seven characteristics from its original design:

  1. Setting—the character of the location and how the bridge is situated in relationship to other features, such as the roadbed and landforms.
  2. Materials—the elements that were originally combined to construct the structure.
  3. Design—reflects the historic function and technology. Design applies to individual structures as well as districts.
  4. Location—the place where the bridge was originally placed or where a historic event occurred. Integrity of location can be extremely important and most historic buildings lose their historical significance if they are moved. Bridges, on the other hand, have traditionally been moved from site to site, so location integrity will not always be a disqualifying issue.
  5. Workmanship—evidence of the builder’s craft skills and technology.
  6. Feeling—the expression of the aesthetic or historic sense of a particular time period.
  7. Association—the direct link between an important historic event or person and the bridge. Association requires the presence of physical features to convey the relationship.

The heritage resource specialist completes the initial recording of the bridge and associated features, such as roads, landscapes, etc. He or she also completes the initial historical background research for the bridge and then applies the criteria for evaluation and determines the level of integrity. The bridge engineer can be an excellent resource concerning the bridge history, past maintenance practices, and technical issues. However, the heritage resource specialist, in consultation with the respective SHPO, is responsible for making the final recommendation for NRHP eligibility.


Exceptional Significance

Generally, a property must be at least 50 years old to qualify for listing on the NRHP. However, as with all rules there are exceptions. Cape Canaveral Florida is listed on the NRHP for its association with the nation’s space program. Likewise, the Dallas Book Repository where Lee Harvey Oswald shot President John F. Kennedy is also listed on the NRHP. Occasionally, bridges less than 50 years old may have exceptional significance and be eligible for the NRHP under the exceptional significance measure.

Bridges less than 50 years old cannot be ignored. Not only could existing bridges be historically significant under the exceptional significance measure, but existing bridges less than 50 years old could become eligible during the repair/reconstruction/construction process. Most State Departments of Transportation (DOT’s) evaluate any bridge more than 45 years old for NRHP eligibility.

The Pugsley Suspension Bridge, which spans the Marias River near Chester, MT, is an example of a bridge eligible for National Register listing because of its exceptional historical significance (figure 2). The Hurdle brothers of Billings, MT, built the Pugsley Bridge in 1951 and it is the only vehicular suspension bridge in the state. The Liberty County commissioners chose this design because site conditions made construction of a steel truss or girder bridge impracticable because of frequent ice jams and flooding. The bridge is 326 feet long with a 290-foot center span (between towers). The towers rise 54 feet above the concrete piers on which they stand. The bridge design is also considered unique because it is a rare example of a braced-cable suspension structure that was designed specifically for this site. Both chords are cables rather than the traditional longitudinal girder or stiffener truss lower chord. The bridge is eligible for the NRHP under criteria A and C.

Photo of the Pugsley Suspension Bridge.
Figure 2—Pugsley Suspension Bridge near Chester, MT.
This bridge is eligible for the National Register of Historic Properties
under criteria A and C as a historic property with exceptional significance.
Photo by Archie Bishop.


Determination of Effect

For each bridge listed, or determined eligible for listing on the NRHP, the Forest Service must analyze the effect an undertaking will have on the bridge and any surrounding historical resources. This analysis of effect must be coordinated with the SHPO.

Each undertaking has an area of potential effect. This area, as determined by the heritage resource specialist and SHPO, is the area physically or visually affected by the proposed undertaking.

An undertaking has an effect when it has the potential to cause any change, beneficial or adverse, to the quality of the historical, architectural, archeological, or cultural character that qualifies the resource for listing on the NRHP. Many routine maintenance activities, such as painting or deck or guardrail replacement, are undertakings, as well as the more obvious activities, such as bridge replacement.

The effect of a proposed undertaking will be one of three types:

No Effect – If an undertaking results in no change to the characteristics that qualify the bridge for listing on the NRHP either directly or indirectly, then it has no effect.

No Adverse Effect – If an undertaking will have some effect on the characteristics from which the bridge derives its significance, but the expected effect does not meet the criteria of "Adverse Effect," the undertaking will have "No Adverse Effect" on the bridge.

Adverse Effect – An undertaking has an adverse effect when one or more of the following conditions are likely to occur:

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