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Covered Bridges and Historic Preservation in
by Eric Gilbertson, Deputy State Historic Preservation Officer
A Burlington Free Press article from August 26, 1940 stated that since 1927, 432 covered
bridges were removed from the State highways in Vermont. A lot of them went out in the '27
flood, but the rest of them disappeared in the years following. This only counts the bridges on
state highways and does not include those lost on town roads. In 1940 there were 168 covered
bridges left on the State highway system. At that time the writer was very proud that only 12
covered bridges came down in that year. Vermont has lost 168 covered bridges from the State
highway system in the last 60 years. Some of those bridges are not gone but are now on town
roads that were at the time state roads.
I've been working for the state of Vermont in historic
preservation for almost twenty-six years, and we have not, in that time, lost a covered bridge
through demolition in order to make way for a new bridge. That is an excellent record and shows
that in those years issue was not about whether or not to preserve covered bridges. The issue is
now over how best to do it. All those working on the covered bridges recognize that some past
repairs have been made that only marginally met preservation and engineering standards for a
variety of reasons.
Not having accurate or complete information makes good
preservation decisions difficult. For example the "real" strength or actual condition of components
may not be known when we make decisions on bridges. There is also an "engineering gap," with
covered bridges that often leads to a much lower load rating than the bridge carries on a regular
basis. This may come from using low strength estimates for the wood in the bridge rather than
more accurate values based on observation and analysis of the actual wood species and quality
found in the bridge. It may be because wooden bridges are very complicated structures where
loads are transferred from one member to another in unexpected ways because of the resiliency of
the wood or the way the pieces are joined to one another.
Therefore a traditional engineering analysis may show a
capacity far lower than the actual capacity. Potentially inaccurate information that underrates a
bridge impacts preservation decisions because it results in far more work being recommended
than is needed to make the bridge functional. Good preservation calls for as little work and
change as possible to get the job done. Engineering decisions and preservation decisions can only
be as good as the information available to make them.
The Agency of Transportation is testing bridge components
as integrated units rather than as individual pieces to help reduce the "gap" and there is a growing
advocacy for more non-destructive testing of bridge components in place. In addition more care
and consideration is being given to all repairs.
Now and in the future the Covered Bridge Committee
organized by the Agency of Transportation assures that a broad scope of ideas coming from
engineers, preservationists, The Vermont Covered Bridge Society and the towns are taken into
consideration when work is being planned on a covered bridge. The Covered Bridge Committee
reviews all work on covered bridges based on a Covered Bridge Plan that establishes priorities
and best practices for covered bridge work.
We are setting a national example in our approach to covered
bridges. I am looking forward to the best possible preservation decisions being made about the
preservation of covered bridges in Vermont because of the cooperation of two state agencies, the
public and the towns owning the bridges in searching for innovative solutions.
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Joe Nelson, P.O Box 267, Jericho, VT 05465-0267, firstname.lastname@example.org
This file posted February 21, 2002