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Covered Bridges and Historic Preservation in Vermont

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.