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Learn about the history and the why of covered bridges and where you can see them in the Pittsburgh area!
The first covered bridge in the United States was built in Philadelphia in 1805—it was named the Permanent Bridge. Over the course of the next century roughly 12,000 of these iconic American spans were constructed across the country, and while the Permanent Bridge is gone, 750 remain standing today, 47 of them in southwestern Pennsylvania.
In the early 1800s, agriculture and industrialization were growing rapidly throughout the Northeast and the coastal rivers and estuaries were lifelines of trade and communication. But as the coastal population penetrated inland, the many rivers and creeks cutting across the region became barriers to overland transport. Farmers and industrialists alike needed bridges to enable commerce across an increasingly sprawling and disconnected region.
Traditional European building methods wouldn't work in the comparatively harsh North American climate—hot summers and frigid winters created freeze/thaw cycles that would overturn stone pavings—but the dry air meant that wood wouldn't rot, and so it became the building material of choice. The reason to cover these bridges was simple: less exposure to the elements meant the wooden superstructures would last longer.
Covered bridges are differentiated by the types of trusses used to support the roadway. These trusses were often named after their creators, and met with varying degrees of success. One early design, the multiple kingpost truss, consisted of a series of triangular sections supported by a central vertical ''kingpost'', and could span up to 100 feet. The Burr arch truss, named for its inventor Theodore Burr, was one of the more popular, featuring two large wooden arches connected to a kingpost truss framework. There are 123 bridges remaining in Pennsylvania using the Burr truss design —more than all other truss designs combined. Nathaniel Town created the Town truss, a latticework of smaller timbers that could be constructed by unskilled laborers and span distances of up to 200 feet. The Theodore Burr Covered Bridge Society has a comprehensive online resource of truss types.
PA covered bridge society with extensive information on bridge terminology and explanations of the different truss types.