Apart from world-famous structures like Brooklyn Bridge or the Golden Gate, the covered bridge is probably the highest profile type of historic bridges in the USA. America has more covered bridges - around 800 - than any other country. Despite being subject to destruction by arson and acts of God, these bridges enjoy a recognised status, being admired by ordinary citizens and engineers, and generally protected by public officials. There is a national programme to rehabilitate America's covered bridges, but the true bridge heritage at risk is the metal truss.
Iron truss bridges evolved from the wooden truss form; the first iron bridges were frames like the Howe and Pratt trusses. Early designers such as William Howe, Thomas and Caleb Pratt paid little attention to European precedents instead developing their own metal truss systems independently, as the previous generation of builders had done with wooden bridges.
Though they exemplify fundamental American values of craft, entrepreneurialism, and unbridled invention and creativity, iron bridges have been almost universally disregarded and forgotten, by both preservationist and engineer. As the American frontier moved west, iron bridges helped settlers cross thousands of streams and rivers, reach new markets, and create new businesses. Hundreds of patents were granted for iron bridges in the 19th century, and while many went to trained engineers, others were awarded to the crafters, millwrights and mechanics. These unschooled 'apple-tree engineers' recognised a need and sought engineering solutions that proved to be practical, if sometimes unconventional.
But recent sobering statistics suggest that half, if not more of the USA's historic bridges have been lost in the last twenty years - two decades in which transportation and preservation consciousness was at its highest level. While we are not quite at the stage of having to save the few surviving examples, we are fast-approaching that point.
In an attempt to try and counteract this alarming state of affairs, a group of US bodies held a workshop at the end of 2003 in an attempt to raise awareness of the issues involved and formulate an action plan to address the situation. Some of the suggestions adopted at this meeting are now being acted upon at both national and state level.
The Federal Highway Administration, the SRI Foundation - a non-profitmaking historic preservation organisation - the National Trust for Historic Preservation, and the Historic American Engineering Record of the National Park Service organised an invitation-only workshop of experts to articulate and define the issues confronting historic bridges.
The purpose of the workshop was to articulate and define efficient and economical strategies for historic bridge preservation and management. The invited experts included transportation, environmental and preservation professionals working at the federal, state and municipal levels, civil engineering educators and several historic bridge scholars.
The core of the workshop involved a group discussion of the problems associated with historic bridge preservation and management, leading to a consensus on the key components of these problems, followed by small group discussions to identify possible solutions to these problems. At the end of the second day, the breakout groups reconvened as one and agreed on a set of recommendations to streamline and enhance historic bridge preservation and management nationwide.
Ten primary recommendations were developed, full details of which can be found in the report on the SRI Foundation website [www.srifoundation.org].
There was little debate or difference of opinion over the primary recommendation to the Federal Highway Administration, Congress and the states; that states should be required to develop historic bridge management plans. Management plans are fundamental to saving historic bridges, serving as the umbrella under which other actions such as best practice examples and improving data accessibility would ensure the preservation of the USA's historic bridges.
Management plans should be bridge-specific rather than a series of vague, general recommendations, and every attempt should be made to identify those bridges where rehabilitation/preservation is appropriate and feasible and to develop specific treatments for these bridges. This recommendation follows logically from the completion of the state-wide historic bridge inventories that have been completed over the last twenty years.
Another key recommendation was the establishment of a national historic bridge task force; an alliance of engineers, historic preservation professionals, transportation planners and the public, to work with public agencies and private interests to preserve significant bridges through advocacy, technical assistance and education.
The group recommended the development of a web site covering the management and preservation of historic bridges. The vision is to provide a national clearing-house for 'one-stop shopping' for contacts, information, and technical resources on anything pertaining to historic bridges. Over the last few months, Cleveland State University in Ohio has begun to create such a website.
Another aim was to develop a National Cooperative Highway Research Program synthesis to explore the decision-making process on rehabilitating or replacing historic bridges. A research statement was drafted and submitted to the standing committee on the environment during its summer meeting, however the statement was temporarily tabled because of more pressing issues relating to the interstate system. The task force will continue to work with NACE, ASCE, NCSHPO and other groups to demonstrate their support for the research project, and additionally those workshop participants from state DOTs will urge their agencies to support the research proposal.
The task force proposed the development of a national glossary for historic bridges that could be posted on a clearing-house web site, since data accessibility was identified as a critical need by all attending the workshop. Although many states are developing geographic information systems for historic bridges, the common language for discussing and describing such bridges varies from state to state, making it difficult to retrieve relevant information through electronic databases. Three workshop participants volunteered to develop a glossary of terms, nomenclature, or key words describing bridges that would be common to all states.
Workshop participants reiterated the lack of a national historic context on historic bridges as a common and recurring problem thwarting the evaluation and treatment of such bridges. A national historic bridge context would make it much easier to evaluate and treat historic bridges at both the state and national levels. In September this year, NCHRP appointed consultant Parsons Brinkerhoff to begin work on a 12-month study to develop a historic context for the most common 50 historic bridges in the USA. Once this national context is developed, it will be possible to compare and evaluate bridges on a regional or national basis. Funding can then be targeted toward bridges with the greatest historical significance or most feasible preservation priorities.
There is a critical need to organise and make available all data collected as a result of the statewide historic bridge inventories over the past 20 years. This effort would enable the development of management plans that would establish priorities for preservation based on a national historic bridge context, but it will take time a
