Historic Bridge Preservation Plan
Vermont's covered bridges are widely recognized as important cultural, economic, educational, aesthetic,
and historic resources. Most are owned by towns and continue to serve the state's network of roads.
Although public support for preserving them is high, many are vulnerable to well-meaning attempts at
repair that result in inappropriate or inconsistent application of preservation standards.
The factors threatening Vermont's historic covered bridges are complex. For one thing, structural
systems must be adequate for the increasingly heavy volume of traffic and loads that use these bridges.
Unfortunately, the strength of their timber frames is often difficult to calculate. Replacement of original
or existing materials, alterations that force changes to overall bridge dimensions, and reinforcements that
discourage maintenance of original structural systems are the harmful and unnecessary results. In short, the
historic integrity of these bridges is at risk.
The goal of this preservation plan is for Vermonters to be able to say, fifty or a hundred years from today,
that the state's covered bridges are truly historic bridges, not a collection of covered bridges that were
largely rebuilt as new bridges during the close of the 21st century.
To pursue this goal, the Historic Covered Bridge Preservation Committee has been established. This committee
will review the status of all covered bridges and make specific recommendations for each, relying on the priority
of uses explained in Part 1 and the priority of treatments explained in Part 2. Organization of the committee and its
responsibilities are described in Part 3. Finally, integration of the preservation plan and the Vermont Historic
Bridge Program is described in Part 4. The committee's recommendations for each bridge will be developed over time,
as required, and will appear in Appendix A. As new recommendations are developed or existing recommendations modified,
Appendix A will be amended accordingly.
The committee has established five principle objectives in developing the plan and its priorities for uses and
Return to table of contents
- The historic integrity of covered bridges should be preserved to the maximum extent possible.
- Covered bridges should remain in use on the state's network of roads whenever possible.
- Towns provide the best opportunities for continued stewardship of covered bridges. Partnerships between
towns and the State of Vermont should be established to assure consistent application of appropriate preservation
- The Historic Covered Bridge Committee will implement this plan through participation in the development and
review of all projects involving historic covered bridges when state or federal funding is used.
- An effective management system must be implemented and sufficient funding obtained. This strategy should be
balanced, on the one hand, identifying bridges in very good condition and maintaining them adequately and, on
the other, identifying bridges in very poor condition and preventing deterioration from becoming irreversible.
PRIORITY OF USES
The following uses for historic covered bridges are listed in order of priority. Preferences have been established
to achieve two objectives. The first is a desire to maintain the historic use of these bridges as part of Vermont's
network of roads. The second is a desire to preserve the structural integrity of historic members of these bridges to
the maximum extent possible. The load capacity for each category varies.
- Special Use on Roads. Bridges will remain in use on roads but will be limited to very light traffic,
primarily cars. This category of use assumes that alternative routes are available or are capable of being built
at locations near enough to historic bridges to minimize inconvenience and to eliminate, or reduce to an acceptable
level, any risk of damage by overweight vehicles. At the same time, alternative routes must not compromise the
settings for these historic bridges. Creative designs for bridge approaches, intended to prevent use by overweight
vehicles, are encouraged. However, these designs must also avoid damage to settings.
Limited Use on Roads. Bridges will remain in use on roads and will be limited to vehicles that do not
exceed 40,000 lbs. This category of use also assumes that alternative routes are available or are capable of being
built at locations that accommodate vehicles weighing in excess of 40,000 Ibs. The proximity of alternative routes,
the degree of risk that bridges will be damaged by overweight vehicles, and the historic structural integrity of
bridges are the decisive factors in choices between Category A and Category B - Limited Use on Roads.
- Structural Integrity. This category of use assumes that the structural integrity of historic members
of these bridges will be preserved to the maximum extent possible. If bridges suitable for this category of use
have been compromised by extensive alterations, they should be restored to their original design.
- Capacity: The capacity sought is the maximum amount obtainable under the preservation treatments
permitted for bridges in this category. Most bridges should be confined to one-lane traffic.
- Preservation Treatments: Superstructure preservation treatments 1, 2, 3 and 4, in that order of
priority, are preferable for brides in this category.
Alternative Transportation Use. Bridges will be adapted to alternative uses at their
existing sites and restored. The setting of the bridge, including its approaches, should be
preserved to the maximum extent possible. This category of use will require alternative routes.
However, the design of any new bridge in close proximity to the historic bridge should avoid
changing the setting of the historic bridge and should avoid interfering with views of the historic
bridge. This category of use assumes that the structural integrity of historic members of these
bridges will be preserved to the maximum extent possible.
- Structural Integrity.This category of use assumes that the structural integrity of historic members
of these bridges will be preserved. If bridges suitable for this category of use have been compromised by extensive
alterations, restoration should be considered.
- Capacity: The maximum capacity for bridges in this category is 40,000 lbs.
- Preservation Treatments: Superstructure preservation treatments 1, 2, and 3, 4, 5, and 6,
in that order of priority, are acceptable for bridges in this category.
Relocation. This alternative presumes that none of the three preceding categories of
use is feasible, and it is an alternative of last resort. Relocation may be considered for any of the
first three categories of use, and all requirements for the category selected will apply.
Bridges Subject to Exceptional Constraints. The circumstances of some bridges pose
exceptional constraints. A few have been so drastically altered that repairs required for an
acceptable carrying capacity would necessitate reconstruction of the entire bridge. In other cases,
bridges have been reinforced by systems that make the historic structure redundant. Bridges
subject to such constraints shall be assigned to this category with the hope that acceptable
alternatives for preservation will develop in the future. During the interim, a greater variety of
preservation treatments are available for preserving these bridges.
Return to table of contents
- Structural Integrity.This category of use assumes that the structural integrity of historic
members of these bridges will be preserved. If bridges suitable for this category of use have been
compromised by extensive alterations, restoration should be considered.
- Capacity: The minimum capacity for bridges in this category is that required to carry
dead load, snow load, and anticipated pedestrian or snow machine loading.
- Preservation Treatments: Superstructure preservation treatments 1, 2, and 3, 4, in that
order of priority, are preferable for bridges in this category.
PRIORITY OF TREATMENTS
The following superstructure treatments for historic covered bridges are listed in order of priority.
Preferences reveal a desire to preserve the historic structural integrity of covered bridges to the maximum
extent possible. Many of Vermont's covered bridges display ingenuity in timber craftsmanship and incorporate
unique treatments designed to address specific problems on specific bridges; this tradition of ingenuity
should be carried forward as well. Prioritization allows identification of treatments that are appropriate
for the specific categories of use. Treatments should be considered in their order of priority to the maximum
extent possible. Treatments should also be applied in order of priority to individual elements of bridges.
- Retain all existing materials that have not deteriorated beyond the point of repair. Where existing rot
or other damage is not severe enough to require replacement, the materials should be repaired rather than
replaced. This treatment should be applied to each member individually, and deterioration of a large number
of bridge elements should never justify the replacement of any single member capable of being repaired.
- Replacement of existing materials in kind, meaning identical in species, quality, and dimension
to the maximum extent feasible, or restoration of original materials and design. Prefereably,
material origins should be from the Northeast region of the country. If a different species or
quality is considered and/or materials from the Northeast are not available, substitutions may be
considered with justification.
- Application of historic methods of strengthening such as the application of sister lattices in
Town lattice truss bridges.
- Introduction of glu-laminated beams as a co-functional, reversible structural system. The
beams must be designed to work in conjunction with the historic structural system to achieve
required load capacity, and the historic structural system must be restored according to
Preservation Treatments 1, 2, and 3.
- Replacement of limited pieces of existing load-bearing members with materials identical in
species, quality, and origin, preferably from the Northeast region of the country, to the maximum
extent feasible. Dimensions may be larger but must not cause alterations to the dimensions of any
other important bridge components. For example, increasing the depth of bottom chords of Town
lattice trusses may increase capacity without requiring alteration to either overall bridge dimension
or the design of the floor system.
- Replacement of existing load-bearing members with glu-laminated members (beams or
chords) of identical dimension.
- Reinforcement of existing load-bearing members with non-obtrusive modern materials such as
steel rods or plates, glass fiber, carbon plates, or other materials.
- Protection of load-bearing members by the introduction of steel beams that provide a
safety-net for the bridge. The redundant structure must allow the existing timber frame to
continue functioning, and a minimum clearance between steel beams and floor beams should be
designed. The purpose of this treatment is to protect the historic bridge in case of structural
failure, not to increase carrying capacity.
- Replacement of load-bearing members with, in order of priority: (a) timber of larger
dimension but otherwise identical in terms of species and quality; or (b) timber of larger dimension
and different species.
- Replacement of existing load-bearing members with modern materials.
The following substructure treatments for historic covered bridges are listed in order of priority.
Preferences reveal a desire to preserve the historic structural integrity of these abutments to the
maximum extent possible and to use masonry materials that are consistent with existing materials whenever possible.
Return to table of contents
- Masonry abutments, whether rubblestone or ashlar, shall be retained whenever possible and repaired rather
than replaced. Repairs should be undertaken with like-kind materials, and all repointing should apply appropriate
mortar. Bearing seats should be repaired in kind whenever possible. Drainage tubes or weep holes should be
installed to channel runoff in all cases to avoid hydrostatic pressure behind the abutments.
- If masonry abutments, or portion of abutments, have deteriorated to the point where repair with like-kind
materials is not feasible, alternative materials may be considered. Where abutments have been undermined by
stream flow, concrete underpinning may be installed. Where bearing seats are inadequate, concrete caps may be
- If masonry abutments have deteriorated beyond the point of repair, they may be reconstructed with modern
materials such as concrete. Ornamental treatments to produce texture such as veneers, form liners, acid
washing, pneumatic blasting, bush-hammering, mechanical stamping or special form-work may be considered.
- Existing concrete abutments should be repaired whenever possible or replaced in kind if deteriorated
beyond the point of repair.
HISTORIC COVERED BRIDGE COMMITTEE
Mission. The mission of the Historic Covered Bridge Committee is to insure that the historic integrity of
Vermont's covered bridges is preserved to the greatest extent possible. Toward that end, the committee must balance
the needs of each project, including historic integrity, traffic volumes, vehicle weights, overall traffic needs, and
Composition. The permanent members of the committee shall include the Vermont Agency of Transportation
(VTrans) Structures Engineer, the VTrans Bridge Management Engineer, the VTrans Historic Preservation Officer, a
VTrans special consultant, the two Co-Managers of the VTrans Vermont Historic Bridge Program, and two designees from
the Vermont Division for Historic Preservation.
Meetings. The Co-Managers of the Vermont Historic Bridge Program shall call meetings and prepare a record
of committee discussions and recommendations. Copies of meeting records shall be distributed to each participant after
the conclusion of each meeting. VTrans project managers and staff will be invited to attend meetings when specific
projects are being discussed.
Town Participation. One or more representatives from a town owning a covered bridge may be invited to
attend any committee meeting convened for the purpose of making recommendations for appropriate uses or preservation
treatments concerning that bridge.
Participation by Other Organizations and Individuals. The committee may invite other individuals or
organizations to participate in meetings concerning specific projects. Such participants may include, but are not
limited to, local historical societies, timber-frame restoration specialists, and the Vermont Covered Bridge Society.
Recommendations and Coordination with Section 106 of the National Historic Preservation Act of 1966 and its
amendments. Committee recommendations reached by consensus of all participants are desirable. In the event that
consensus is not achieved, a recommendation will be reached by vote. Permanent members each will be entitled to one
vote. Towns owning the bridge in question will be entitled to one vote. The committee recommendation will be recorded
and notification given to the VTrans Project Manager. Objections raised at meetings by non-voting participants will
be noted in the record. Any voting participant may request further review of the recommendation and may take advantage
of the provisions for resolving disputed projects, as outlined by the Vermont Historic Bridge Program Programmatic
Agreement dated July 7, 1998.
Committee recommendations meet the Secretary's Standards for Rehabilitation and therefore are consistent with the
requirements of Section 106 of the National Historic Preservation Act (Section 106). The VTrans Historic Preservation
Officer is responsible for reviewing federally funded covered bridge projects under Section 106 through a "Programmatic
Agreement ... Regarding Implementation of the Federal-Aid Highway Program in Vermont." (PA). Committee recommendations
will be recorded in matrix format and will be attached to the letter prepared by the VTrans Historic Preservation Officer
as required in the PA. The letter will state that if circumstances necessitate departures from Committee recommendations
or if there are significant project changes, the VTrans Historic Preservation Officer will justify and document them in
writing. The VTrans Historic Preservation Officer may consult with individual members of the Committee or the entire
Committee regarding project changes that might arise after the Committee's review of the project.
Responsibilities. The committee will oversee implementation of the Historic Covered Bridge Preservation Plan
and its incorporation into the Vermont Historic Bridge Program. Specific tasks will include:
- Preparing and advocating for an agenda that fully funds and implements this plan as part of the Vermont Historic
- Identifying suitable funding programs for special needs such as stabilization and repair of bridges threatened
- Submitting recommendations for assigning each historic covered bridge to a specific category of use together
with the appropriate preservation treatments applicable to that category.
- Advocating that a plan is prepared for the maintenance and repair of each historic covered bridge.
- Resolving any conflict among various parties concerning specific bridge projects.
- Participating as needed during both the design and construction phases of each bridge project affecting an
historic covered bridge.
- Participating in presentations to the VTrans Transportation Research Committee when appropriate.
- Evaluating the merits of innovative products and ideas available for the preservation of historic covered bridges.
- Such other tasks as the committee, from time to time, determines are appropriate.
Communication. Participation by the committee is vital, and the committee must be given adequate information
to determine whether design proposals are appropriate. Effective methods of communication with engineers, contractors,
town officials, and members of the public who work with historic covered bridges are essential. Toward that end:
Return to table of contents
- Project managers assigned to work on specific bridge projects should provide all
documentation necessary for committee consideration. This may include, but is not limited to:
- identification of all major structural problems and major failures;
- estimates of structural capacity assuming all components are in good condition; and
- engineering standards for determining all features and materials to be replaced in order to achieve the
- In the case of projects for which detailed plans have not been developed by an engineer, the bridge owner should
require the contractor to provide a detailed statement identifying all features and materials to be replaced. That
report should be supplemented by one or more field inspections by the committee during any disassembly phase.
- Contractors or engineers should notify the VTrans Historic Preservation Officer immediately in the event that
new information is uncovered during the construction phase.
- Towns should notify the committee about any proposed work prior to the commencement of that work.
INTEGRATION OF HISTORIC COVERED BRIDGE PRESERVATION PLAN AND THE VERMONT HISTORIC BRIDGE PROGRAM
Ownership of Bridges. Partnerships among the respective towns, the Vermont Agency of Transportation (VTrans)
and the Vermont Division for Historic Preservation (VDHP) are the preferred methods of stewardship. Towns will remain
owners of these bridges but may enroll them in the Vermont Historic Bridge Program when projects involving substantial
repairs are developed, provided bridges remain in highway use. Enrollment will take place when an easement agreement has
been conveyed from the town to VTrans, formalizing the town's commitment to preserving the bridge in perpetuity for highway
use. After bridges have been enrolled in this program, VTrans will pay for all future costs of rehabilitation and major
maintenance to the extent that federal and/or state funds are available for such work. VDHP will cooperate with VTrans
in monitoring compliance with the preservation easements. Towns will be required to conduct the following routine
maintenance tasks as part of the easement agreement:
- Cleaning bridge components with compressed air and removing with hand tools any deposits of debris or dirt that
may hold moisture.
- Keeping drainage areas free of debris and channeling deck drains and approach run-off away from bridge elements
- Removing all small trees and shrubs growing in, on, or near substructure units or under bridges.
- Removing any debris that accumulates in the channels beneath bridges.
- Maintaining proper load posting and advance warning signs and keeping all signs visible.
- Maintaining a water-tight roof system and repairing any damaged siding.
- Removing any accumulated snow when such snow is of a depth to cause concern for the stability of the structure.
- Maintaining smooth transition between approach roadway and bridge decks, maintaining straight and continuous
rails, and repairing minor damage caused by accidents.
- Reporting significant problems concerning bridges to the co-managers of the Vermont Historic Bridge Program
and to the appropriate District Transportation Administrator.
- Consulting with the co-managers of the Vermont Historic Bridge Program prior to initiating any emergency repairs.
All historic covered bridges owned by the State of Vermont will become part of the Vermont Historic Bridge Program
upon execution of this preservation plan and are the responsibility of state government. Partnerships between state
agencies owning covered bridges may be developed in the future to address the question of financial responsibility
for maintenance and rehabilitation.
Public Education. Success of the preservation plan will depend on public awareness about the value of
Vermont's covered bridges and about threats to the historic integrity of these bridges. Toward that end, the program and
other departments in VTrans should collaborate with VDHP to accomplish the following:
- Educate towns about the importance of consistent preservation treatments for the state's collection of
covered bridges and encourage town officials to enroll eligible bridges in the Vermont Historic Bridge Program.
- Establish and enforce a consistent policy regarding state and federal funding for town-owned covered bridges
that are not repaired according to treatments recommended by this preservation plan.
- Increase public awareness about the need to enforce load restrictions on historic bridges, undertake any
legislative initiatives required to assure enforcement, and develop attractive, familiar signage that will
notify track drivers at appropriate locations to select alternative routes.
- Conduct periodic training programs for state employees, town officials, and other interested individuals
or organizations covering a broad range of topics, including but not limited to project administration and
Objectives. Success of the preservation plan will also depend on continued growth of the Vermont Historic
Bridge Program and its ability to address the specific concerns associated with preservation of covered bridges.
Toward that end, the following should be accomplished:
Return to table of contents
- Develop VTrans engineering expertise in the preservation, restoration, and rehabilitation of historic
- Develop the ability to apply new technology and treatments to the preservation of historic covered
bridges, as those technologies and treatments become available.
- Conduct research and develop design specifications for the preservation, restoration, and
rehabilitation of historic covered bridges. Research should focus on analysis of structural materials
and the interaction of components and should lead to evaluation of structural components in place
through non-destructive testing.
- Develop design specifications for the construction of new timber framed covered bridges and
the rehabilitation of existing historic covered bridges.
- Prepare design criteria for roadway approaches to historic bridges that remain in use on the
state's network of roads and for bridges that are placed in alternative transportation uses. Criteria
should address a number of issues including, but not limited to, discouraging large vehicles from
using these bridges. For bridges in alternative transportation use, criteria should seek to preserve
the bridge's original setting to the greatest extent possible.
- Develop an appropriate policy for privately owned historic covered bridges. Preservation of
these bridges is desirable, but a public interest in these structures must be assured through
partnership agreements, preservation easements, or outright conveyance. Legislative initiatives
may be necessary to achieve these objectives.
Federal Highway Administration
Signed 4/10/03 by Division Administrator
Vermont Agency of Transportation
Signed 4/02/03 by Secretary
Vermont State Historic Preservation Officer
Signed 4/07/03 by S.H.P.O.