Swing-span Smith Creek Bridge (New Hanover County Bridge 29) designed by the State Highway Commission in 1930 to carry Castle Hayne Road/Old NC 133 into Wilmington (Durwood Barbour Collection of North Carolina Postcards, UNC-Chapel Hill)
North Carolina's coastal region, with its many sounds and navigable waterways, has a long history of movable bridges equipped to change position to allow the passage of marine traffic. Movable bridge technology dates to the Medieval period in Europe, with the earliest being simple drawbridges that were hinged at one end and lifted at the other by ropes or cables pulled by hand or windlass. One of the first movable bridges in North Carolina was built about 1768 over the Northeast Cape Fear River on the Duplin County Road north of Wilmington. Although movable highway bridges have been in use in North Carolina since the colonial period, no early examples have survived.
Movable bridges are inherently complex structures because of the requirements of moving. The structure must be able to withstand stresses in both the closed and opened positions, and it must have a power source and transmission system to open the span. Furthermore, operators must be on hand to control the bridge and to monitor the safety of both the traffic on the roadway and in the marine channel.
Single-leaf bascule bridge over the Albemarle Sound in Edenton, ca.1910 (Courtesy of The State Archives of North Carolina)
Movable bridge technology remained in a relatively primitive stage until the 19th century, when it progressed rapidly due to advances in mechanical and civil engineering and the availability of new power sources such as steam engines and electric motors. Since the early 20th century, several relatively efficient and simple-to-operate movable bridge types have been in use in the United States, including North Carolina.
Movable bridges are classified by the way they are raised, turned, or lifted. All of North Carolina's surviving examples are swing spans or bascules, two of the most common types. North Carolina's Historic Bridge Inventory includes eleven movable bridges with dates of construction from 1928 to 1960.