Medora Covered Bridge
Another way to measure is the siding at the floor. The most consistent measurements are: MCB 459'3" and the CWCB 449'5".
It must be pointed out that for most casual observers, the length of the bridge is the roof length. According to David Fischetti, the Architect for the 1988 rebuild of the CWCB, and the sign in front of the bridge, the roof length is 460'.
Jim Barker cites the roof length of the MCB at 461'. Independent measurements for the MCB by Bill Cotterman, an Archchitect from Indianapolis, the Jackson County Sheriff's department and at least three others, show the roof length at 461'3".
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. Two other covered bridges claim to be the longest and both are historic. Which one is longer depends on the standard of measurement.
The Cornish Windsor Covered Bridge (CWCB) over the Conneticut River between New Hampshire and Vermont has always claimed to be the longest. That was not disputed until recent years when Jim Barker P.E., who has created the drawings for numerous covered bridge rehab projects, raised questions about the criteria for measuring. Barker asserts that the Medora Covered Bridge (MCB) over the East Fork of the White River in Southern Indiana is longer based on specific measurements.
The argument is fairly simple. The CWCB measurement is based on the lattice length citing that the lattice is functional into the overhangs and the MCB overhangs are not functional except for weather protection. This measurement favors the CWCB 449.5' to 434' for the MCB.
Barker asks: "What is being accomplished when building a bridge?" His conclusion is that a void is being crossed. Barker contends that what determines the length of that void is where the abutments are placed, taking into account the changing water levels of the river.
According to Barker, the length between the face of the abutments of the MCB is 430'4". The New Hampshire Department of transportation cites the length between the abutments of the CWCB at 422'.
In the design of the MCB, because the arches rest on the face of the abutments and the piers bearing the brunt of the weight of the bridge, the framework does not need to extend beyond the face of the abutments to be stable.
The Town Lattice design of the CWCB is above the pier and the abutments. Because the lattice design uses several interlaced systems of diagonals, it is necessary that all points of the lattice extend beyond the face of the abutments in order for all systems touch down.
Barker contends that extending the lattice does not extend the length of the gap that is being crossed. His conclusion is that the true length of the bridge is abutment face to abutment face and not the length of the framework.