World Guide Covered Bridge (WGCB) numbers have been assigned by the National Society for the Preservation of Covered Bridges (NSPCB) are referenced for all listed bridges.  Assigned numbers are coded, such as NH-05-12 or VT-115-a.  The first two characters are the postal abbreviations for the state (formerly digits starting at 01 represented the state in alphabetical order).  The second two digits represents the county in alphabetical order starting at 01 for each state.  The third pair of characters represents the bridges place in the NSPCB tally of that county's bridges, starting at 01 for authentic truss type bridges or a letter for non-authentic type bridges, an upper case letter for motor vehicle bridges, and a lower case letter for footbridges.  Additionally, bridges that have a leading "(" before the last letter, are considered O.C.B.I. - "Of Covered Bridge Interest" - a Covered Bridge that is under 12' or is just on the ground and not over anything, i.e., 45-12-(b.

Massachusetts - General information. There were large wooden arch bridges built across the Merrimack River in the northeast corner of Massachusetts as early as 1792. The shorter of the two spans crossing the Merrimack River was covered in 1810. At one time Massachusetts had over one hundred covered bridges that spanned the numerous waterways in the state. At least eight of them stood in the Connecticut River Valley. Today, only seven historic covered bridges are still standing. The normal ravages of time and nature - floods, ice, and wear account for many of these loses; others have been lost to arson or neglect. Among the seven surviving historic spans, the fate of at least five is in question. This seems to be largely due to a lack of concern.