Truss 1Bridge to the Past:

A Management Plan for Pennsylvania’s Historic Metal Truss Bridges

Management Summary


An important part of the Commonwealth of Pennsylvania’s heritage was our leading role in the story of the Industrial Revolution.  The modern processes of iron and steel production and fabrication were in part born in the great foundries and works at Pittsburgh, Bethlehem, and other parts of the state.  A durable legacy of that heritage of iron and steel, one that every Pennsylvanian is familiar with, is our population of  metal truss bridges. These spans of wrought iron and steel date to the late 19th through the mid 20th centuries, and have connected Pennsylvania communities to each other and to the larger transportation network for more than a century. Pennsylvania has, by many accounts, the earliest, most diverse, and most significant population of metal truss bridges in the United States.  Generations of Pennsylvanians have heard their tires sing on the metal decks, seen a river or railroad pass below, fished over the railings, or watched the sun descend behind an old truss.  Some of these bridges are iconic parts of Pennsylvania’s historic communities, and are fondly recalled symbols of many of our hometowns and communities.

These bridges are also components of the state’s modern transportation network.  For many of them, that has proved to be their undoing. Most were never designed with an anticipation of the volume and size of modern traffic, nor were they designed to last as long as some of them have. Decades of limited maintenance funding have also taken their toll, and many bridges show the signs of their age, and are succumbing to the wear and tear. They also don’t conform to modern standards of safety: all of them have fracture-critical members. The result has been an accelerating rate of loss through replacement. Since 2001, and as of April 2018, 44% -141 out of 321 metal truss bridges that were  listed in or were determined to be eligible for listing in the National Register of Historic Places (NR) prior to 2016 - have been replaced.  

The heritage value of these bridges presents a set of both challenges and opportunities to the Pennsylvania Department of Transportation (PennDOT). As the agency responsible for Pennsylvania’s transportation network, PennDOT is required by federal and state law and regulation to both maintain a safe and efficient modern transportation network, and to do what it can to preserve and extend the useful life of our legacy of historic truss bridges.  These requirements drove the development of this plan.

 The goal of this plan is to take sensible measures to extend the useful life of historic truss bridges: to “manage assets” through routine maintenance and repair.  We seek to maximize the chances that historic bridges that can be rehabilitated to meet the transportation need are preserved and remain in transportation use.   In addition, in cases where important bridges cannot be rehabilitated to meet a transportation need, but can be moved, we seek to encourage their adaptive reuse at another location for alternative uses such as pedestrian or bike traffic.  As a planning tool, we propose to evaluate these historic metal truss bridges, on an individual bridge basis, prior to their being programmed on the State Transportation Improvement Program (STIP) to assess their potential for successful rehabilitation and establish a level of priority based upon a thoughtful understanding of the significance of the bridge.  Finally, we seek to treat historic metal truss bridges as a population and strategically plan for their collective futures, rather than address their potential for rehabilitation without reference to the entire population, one at a time, during preliminary engineering. This plan has been developed in consultation with our partners at the Pennsylvania State Historic Preservation Office (PaSHPO) and the Federal Highway Administration (FHWA).

Using the Plan

A large and disparate group of stakeholders have some interest in the issue of truss bridge management and preservation, and some of those interests diverge considerably. 

There is a large community of technical subject experts who need guidance and who have defined responsibilities in the process of managing truss bridges. Those experts include:

  • Public and Private sector Engineers and transportation agency staffers (FHWA, PennDOT, Community and Transportation Planners (including Metropolitan and Rural Planning Organization Staff)
  • Attorneys and Legal Staff

    Similarly, there are many other subject experts and interested parties with a stake in the management and future of truss bridges.  Their interests and areas of expertise are quite different than the user-communities listed above, and they bring a very different set of expectations and perspectives to the management of truss bridges.  They include:

  • State and Federal Agencies with consultation roles or shared interests on this issue (the PaSHPO, the Advisory Council on Historic Preservation, the Pennsylvania Department of Conservation and Natural Resources [DCNR], etc.)
  • Emergency Services Providers
  • The Historic Preservation community
  • The Trail community
  • Elected officials and county and local government officials and staff.

Since these two groups of stakeholders may have somewhat different interests, responsibilities and areas of expertise, the plan attempts to provide guidance that both the technical and more generalized stakeholders can use.  In some cases, certain technical terminology will be defined in an appended glossary   Some sections of the plan are also explicitly directed at one community of users or the other, although every attempt has been made to make every section as accessible and readable as possible.

Elements of the Plan

National Register Evaluation and Prioritization

As of April 2018, there are 414 metal truss highway bridges remaining in Pennsylvania, a 51% loss since 2001 when there were 851 metal truss bridges.  As the population of these bridges continues to age and decline, the remaining bridges continue to be evaluated, or reevaluated, for their National Register of Historic Places.  status, both as individual structures and as potentially contributing parts of larger National Register Historic Districts. Ultimately, National Register eligibility or listing is one of the important criteria for further consideration of efforts to preserve truss bridges.  PennDOT conducted a statewide historic bridge inventory and evaluation between 1996 and 2001 which resulted in consensus with the PaSHPO regarding the individual National Register eligibility of all state and locally owned bridges in PennDOT’s Bridge Management System (BMS).  A re-evaluation of metal truss bridges was conducted in 2008, and another was finalized in spring 2018.  As a result of the 2017/2018 reevaluation, 54 bridges were evaluated as National Register eligible, resulting in a total population, as of May 2018, of 210 National Register eligible or listed metal truss bridges; this number reflects the removal of 13 previously eligible bridges that were determined not eligible in this reevaluation, 1 bridge determined not eligible by the Keeper of the National Register in 2010, and 10 eligible bridges that were moved or adaptively reused.  The status of a bridge in terms of National Register eligibility as a contributing component of any historic district or site is on-going and generally occurs in relation to a project.

State and federal law and regulation afford equal consideration to all historic bridges.  That said, the National Register recognizes a hierarchy of importance, including the concept that some properties are “exceptionally important”.  The priority protocol in this plan recognizes these differences and categorizes the historic trusses as exceptional, high, or moderate priority.  The priority protocol aids in planning decisions and facilitates appropriate mitigation and minimization measures during preliminary engineering, final design and/or construction.

Evaluating Preservation Potential

Following National Register evaluations, the next step in the plan was the establishment of a benchmark for evaluating the preservation potential for each bridge as part of the transportation network.  In general, that benchmark focuses on whether a bridge can, either through rehabilitation or maintenance, meet a benchmark of 15 tons (usually  the minimum acceptable load carrying capacity for rehabilitated structures) and still retain its National Register integrity .  Where a bridge is clearly designed for vehicular loads less than 15 tons a lower benchmark was utilized.

Preservation Assessments

Individualized evaluations for each historic bridge, known as preservation assessments, were developed to fully evaluate the ability of the bridge to meet the benchmark. These include baseline information on  bridge location, ownership, type and design, year built, dates of alterations and/or rehabilitations, width/length, number of spans, roadway classification and type of service, level of historic preservation priority and justification, character defining features, setting description, average daily traffic, observed crash history, safety features, proximity of alternate routes, summary of geometric deficiencies, hydraulics, condition rating, load ratings, and a summary of structural deficiencies. The assessments also include options for addressing structural deficiencies, including maintenance and rehabilitation to the Secretary of Interior’s Standards, in order to meet the benchmark load capacity.

Maintenance Manual

A guidance document for the maintenance of truss bridges has been prepared as part of this plan. The maintenance manual provides recommendations for specific kinds of regular care (for example, simple annual washing of bridges subject to salt and the elements to slow or prevent corrosion) that can greatly extend the useful life of truss bridges.

Planning, the National Environmental Policy Act, and Historic Truss Bridges

The life cycle of all transportation projects begins with planning, progresses to design and into construction, and then integrates regular maintenance into completed infrastructure. Traditionally, the studies and evaluations required for projects to comply with the National Environmental Policy Act (NEPA) and other environmental laws and regulations, including Section 106 of the National Historic Preservation Act (Section 106), have always been done during the design phase of projects, after earlier stage planning decisions have already been made. For more than a decade now, federal transportation law and policy has been promoting the concept of integrating some of the environmental work for transportation projects into the earlier planning stage of project implementation.   This initiative is known as PennDOT Connects in Pennsylvania or what the FHWA terms Planning and Environmental Linkages (PEL).  In the most basic sense, the consideration of the environmental effects of proposed projects as early as possible in project planning should result in projects that have more realistic budgets, that better address transportation needs, and that have less dramatic effects to all kinds of environmental resources, including heritage resources.

The Truss Bridge Management Plan included an explicit effort to integrate historic truss bridge management with PennDOT’s existing planning program aimed at better establishing transportation needs at the particular crossings where the historic metal truss bridges exist.   This effort included a number of elements which involved direct outreach to stakeholders including county or municipal bridge owners, MPOs and RPOs, historic preservation groups and advocates, and other stakeholders. PennDOT held 27 meetings statewide to discuss over 80 bridges. Meetings with these stakeholders resulted in a valuable exchange of information.  Bridge owners learned about the history and significance of their bridges and insight on options for preservation or other project advancement in the future.  PennDOT also collected information from local sources regarding issues and use of the bridge crossing (transportation needs or lack thereof), as well as future plans for the bridge if known.  Adaptive reuse was also discussed, whether it be at a bridge’s current location or at a new location.  Information gathered at the local outreach meetings and from the preservation assessments was used to complete PennDOT Connects Screening Forms for each of the bridges.  These forms serve as a transportation planning tool for proposals (potential future projects) being initiated by the MPO/RPO and for Asset Planning proposals from PennDOT.

Outreach is ongoing to other state agencies and organizations to identify adaptive reuse opportunities at locations like trails and parks. 

This effort helps insure that when projects move from planning to design, project designers have all the tools and options available to implement projects that maximize the preservation opportunities for historic truss bridges.


The plan anticipates the need for funding beyond simply addressing each individual bridge’s needs.   FHWA and PennDOT are investigating a program that could include line item(s) dedicated to the management of historic metal truss bridges.  Alternatively, or in addition, mitigation dollars from replaced historic bridges could be banked into a dedicated fund to help cover historic truss rehabilitation and relocation activities.

Preservation Partnerships

The plan anticipates the development of partnership opportunities with agencies and non-profits in the land management, trail and preservation communities for the adaptive reuse of bridges that aren’t good candidates for preservation and continued use in-place.  Agencies and organizations that manage trail programs or public lands can work with PennDOT to develop a list of needs for their networks, and to try to match suitable available bridges to those needs.   As part of this effort, using funding provided through an inter-agency agreement from the FHWA, in 2016 the PaSHPO hired a staff member for a minimum of three years to assist in the development of partnerships and historic bridge marketing efforts.

National Historic Preservation Act Compliance

Section 106 of the National Historic Preservation Act is the primary federal law that provides for consideration of National Register eligible or listed resources affected by federal actions.  The specifics of how those resources are considered can be agreed to programmatically. Programmatic Agreements (PA’s) can both streamline and clarify the specifics of compliance with Section 106. As a complement to the plan, the need for a Truss Bridge Management PA will be evaluated. If such an agreement will contribute to the successful management of the historic metal truss bridge population and will streamline PennDOT's compliance with federal law and regulation, a PA will be drafted.


Appended to the plan are a variety of practical tools, plan components, and examples that will help promote the goals of proper management and stewardship of historic truss bridges.

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