The Smolen-Gulf Covered Bridge in Ashtabula County, Ohio, is the longest covered bridge in The U.S. It was opened in 2008 meeting modern standards and does not qualify as historic.
The Medora Covered Bridge (MCB) over the East Fork of the White River in Southern Indiana claims to be the longest historic covered bridge in the U.S. based on the length of the span that is being crossed. The abutments at the ends were placed in a position to account for the rise and fall of the river. The assertion is that the true measure of the bridge is the distance between the abutments. The length of the housing depends upon the truss design and can be extended any length but that does not change the length of the void that is being crossed.
The Cornish Windsor Covered Bridge over the Conneticut River betweeen New Hampshire and Vermont claims to be the longest historic covered bridge in the U.S. based on the length of the truss. It is a lattice design which is above the pier and abutments and must extend beyond the face of the abutments to be stable. The contention is that since the truss is used for support, the true measure is the truss.
Actually, the issue is very simple. If the span is the distance between the supports as in the upper example, then the Medora Covered Bridge is longer. If it includes the wire, then the Cornish Windsor Covered Bridge is longer. (Drawings by Nick Walden.)
The word span is extremely confusing. Some feel the span is the distance from end to end of the bridge. Others say it is the truss or bed timber. Still others feel it is the length of the planks. I'm told that in engineering the span is the distance between two intermediate points. That definition of a span will not get you across the river. That is like saying that the span of the hand is the distance between two fingers. So, what do you call the distance between the abutments when piers are added if all these other things are called spans? J. .J. Daniels in the original contract for the Medora Covered Bridge calls it Clear of Span in order to distinguish it from the other terms for span. Daniels says the Clear of Span for the Medora Covered Bridge is 431'10". As for the measurements of the CW Bridge, two intermediate spans of 203' and 204' plus a pier of 15' equal a Clear of Span of 422'.
Medora Covered Bridge