The Poplar Street bridge is a 112’-long, 17’-wide, center-bearing, swing span bridge with a Warren pony truss superstructure. Constructed in 1915, the Poplar Street bridge is Delaware's oldest movable highway bridge. Currently, it is inoperable, although the turning mechanism remains in place. The bridge was operated manually by turning a capstan to engage the rack and pinion mounted on the center pivot pier. The bridge is listed in the National Register of Historic Places as a contributing resource to the Laurel Historic District, once an important rural commercial center with waterfront warehouses and canneries.
Swing span bridges were the dominant movable bridge type in Delaware from the 1870s to the 1910s. The Poplar Street bridge, when built in 1915, was a late example of the movable bridge technology that had been standard for several decades and was being rapidly superseded by the new bascule technology. The bridge pivoted on a center bearing post with eight balance wheels traveling on a circular rack for stability. The Warren pony truss superstructure is composed of standard built-up steel angle and channel sections. Warren pony trusses were a popular early 20th century highway bridge type and were applied to both movable and fixed spans. Two rail high pipe railings are attached to the inside of the trusses. The bridge is supported on concrete abutments and a timber pile center pivot pier.
Little is known about the history of the Poplar Street bridge. Presumably it was constructed under the auspices of the Sussex County Levy Court. It was taken over by the Delaware State Highway Department in 1935 as part of its expanded responsibilities for all former county roads and bridges. In 1946, the state highway department replaced the deteriorated concrete pivot pier with a timber pile pier. The repair plans note that the bridge was built in 1915, and that the swing span was opened about 100 times in 1946. The plans also show that there was a one-story frame operators house located on the northwest embankment.
The Poplar Street bridge was last opened to navigation in 1975. Since that time, it has undergone alterations that have rendered it inoperable but also have resulted in the preservation of the trusses and operating mechanism in situ. In 1994, the Delaware Department of Transportation removed the trusses to have them cleaned and painted. The beams that support and stabilize the bridge when it is opened were replaced in-kind. Original riveted connections were replaced by high strength bolts. The operating mechanism, including gears, shafting, and center bearing, were reset but not returned to operating condition.