A workhorse bridge is a bridge less than 300 feet in length (one or two spans), generally from constant girder-type structures assembled from standard structural components and systems. Such bridges are common in rural areas and the replacement of bridges in rural areas is a common project type for most state departments of transportation (DOTs). When replacing a workhorse bridge that is contributing to a rural historic district, the mitigation usually involves replacing the bridge with a bridge designed to be context sensitive. Yet even when a bridge is not contributing to the historic district, a new bridge that is not context sensitive (i.e., does not follow Secretary of Interior Standards) can have an adverse effect to the historic district. Although for both situations the context is established—a rural historic district—there is little guidance on context-sensitive design responses. Increasingly State Historic Preservation Officers (SHPOs) and the National Park Service are taking a landscape perspective on historic resources, leading to more and larger rural historic landscapes/districts. As a result, state DOTs can expect to address historic context considerations in an increasing number of rural bridge replacement projects.
A preliminary survey of published literatures reveals two types of guidance for workhorse bridge aesthetics: (1) presentation of the principles of bridge aesthetics along with scattered examples (e.g., AASHTO’s Bridge Aesthetics Sourcebook Practical Ideas for Short and Medium Span Bridges); or (2) state DOT guidance documents that address urban settings, highway corridors, interchanges, scenic areas, or challenging engineering issues, but not rural historic contexts.
For workhorse bridges, feasible elements for developing a context-responsive design may be limited to the use of horizontal and vertical lines and shadowing, surface treatments, barrier choices, color, and railings. Yet these elements can make substantial contributions to creating an aesthetically pleasing and context-appropriate bridge design. Further, these elements can vary widely, presenting opportunities for design choices that respond to the historic context.
By its nature, a context-sensitive design approach will produce different design solutions in different parts of the country. Still, there are likely solutions appropriate in many settings. State DOTs will benefit from a resource on context-sensitive design focused on rural historic districts and workhorse bridges. In addition to the bridge design, the resource should provide information on constructability, construction cost, and maintenance requirements. These practical considerations can help ensure the mitigation is commensurate with the impacts. The resource also should cover how historic context can be integrated into the overall design process, rather than treating context as an add-on or afterthought. A practitioner-ready resource can support effective consultation by presenting examples of successful designs so all partners to better visualize the outcomes, estimate costs, and understand the implications for future maintenance.
The objective of this research is to develop a practitioner-ready resource of context-sensitive design examples appropriate for workhorse bridges in rural historic districts.