Historic Bridges

The State of Vermont’s Division for Historic Preservation owns five covered bridges and two metal bridges. The history of bridges in Vermont dates to the development of the state’s earliest roads. 

Covered Bridges 

Vermont’s covered bridges are landmark centerpieces of a quaint setting of rural New England. A covered bridge is a timber structure supporting a deck surface that carries loads over an obstruction, such as a river, stream, railroad, or roadway. The typical covered bridge uses heavy timber trusses to carry loads with a floor system spanning between the longitudinal trusses and weight distributed and carried between those trusses. The primary purpose of the roof is to protect the structural timbers from the ravages of weather. The roof preserves the supporting trusses, which without the covering would fail in a few years because of rot and deterioration in a time when treated woods were not available. Bridge builders quickly recognized that simply putting on a roof paid off in the end financially. Other reasons for covering the bridge structure: 1) the added support of side-supporting trusses, walls, and roof provided internal bracing that tolerated lateral loads from wind; 2) the walls and roof provided the necessary security to calm animals crossing rushing waters, which scared livestock and caused stampeding. The high windows allowed drivers to see oncoming traffic is located on a curve, as well as provide natural light.

During the 19^th century the number of covered bridges in Vermont reach over 700. The horrendous flooding of 1927 destroyed approximately 100 covered bridges. Thirty-five covered bridges once spanned the Connecticut River. By 1940, as the automobile became the primary mode of transportation, less than 200 covered bridges endured. Documentation efforts record that by 1996, only 106 covered bridges remained in Vermont.

The Federal Highway Administration completed a study identifying 880 covered bridges dating from the 1820s to 1987 in thirty states. The survey recorded that Pennsylvania and Ohio retained the most (227 and 143, respectively). Vermont was ranked third nationally with 100, dating from 1820 to 1982. Vermont has the most covered bridges per square mile than any other state. Ninety of those covered bridges have been listed in the National Register of Historic Places. In 2014, Brown Bridge (1880) in Shrewsbury was recognized as a National Historic Landmark because it is an outstanding example of Town lattice truss and was the last bridge built by preeminent bridge wright Nichols Powers. 

Metal Bridges 

Iron truss bridges became popular in Vermont after the Civil War. The iron was more durable, able to counter the stresses of tension and compression, and was certainly resistant to fire.

America’s first truss bridges built entirely of iron were erected in 1840 and 1841 to span the Erie Canal. Railroads quickly recognized the advantages of the material with the first metal truss bridge completed in 1845; Vermont railroads shifted to iron bridges after 1870. According to Robert McCullough in Crossings: A History of Vermont Bridges, Vermont’s first iron truss bridge was probably erected in Bennington sometime before 1866 and possibly as early as 1857. In Vermont, the first metal bridge fabricator was the Vermont Construction Company, a subsidiary of the R.F. Hawkins Iron Works of Springfield, Massachusetts. By 1887, approximately twenty-one iron bridges were spanning Vermont.

Standardization in bridge design by the turn of the 20^th century have precedent with the Pratt (1844), Warren (1848), or Whipple (1847) trusses. The growth of rail transportation continued to generate experimentation and invention, especially with the need to span greater distances. In Germany and other parts of Europe, the lenticular or parabolic truss had been promoted during the mid-19^th century for greater distances and durability. The design relied on curved upper and lower chords, giving the trusses the shape of a lens. The upper chord provided maximum depth at the center space, with the bottom chord continuing little or no additional strength. This changed when lenticular trusses were employed on through bridges where nearly all the floor beams were carried by the bottom chord with additional support provided by vertical rods. The initial patents were granted in 1878 and 1884 to William O. Douglas, who produced the plans for most of the lenticular spans in America. S.C. Wilcox, president of the Corrugated Metal Company, purchased the initial patent. He developed a successful bridge division and renamed the company, Berlin Iron Bridge Company. Wilcox’s successor, engineer Charles Jarvis, utilized both of Douglas’s patents, adding “Douglas and Jarvis Patent” plates to the bridges.

The most elegant of the lenticular truss bridges in Vermont is the Highgate Falls Lenticular Truss Bridge. It relies on a through system for the long main span and a pony truss for the shorter approach span. It was erected by the Berlin Iron Bridge Company in 1887. The main span is 215 feet and the pony truss approach span is 80 feet.

Coinciding with the organization of Vermont’s transportation system, the town of Wilmington contracted to have the Medburyville Bridge constructed in 1896, replacing a c. 1855 wood bridge. The cost of construction by the Vermont Construction Company was $1,513. It remains as one of two double-intersection Warren through trusses in Vermont.

For more information on Bridges and Covered Bridges click on the links below 

Historic Context for Covered Bridges
Historic Context for Railroad Bridges