River Road Bridge

Information and Findings From New Jersey's Historic Bridge Inventory

Discussion of Bridge (Prior To Alteration)

Summary: The two-span, six-panel, riveted Pratt pony truss bridge has concrete abutments and cutwater pier. The bridge is one of the least altered of over 15 pony trusses built between ca. 1900 and 1927, and it is the only rivet-connected Pratt pony truss in the county. It is a well preserved example of a historically and technologically significant type that is becoming increasingly rare in the state. The riveted Pratt is not a common 20th-century pony truss type, which adds to the value of the span.

Physical Description: The 180'-long bridge consists of two six-panel half-hip Pratt pony trusses of equal length. The trusses are rivet connected rolled steel sections. The upper chords and inclined end posts are built-up box beams with cover plates. The lower chords, verticals, and diagonals are angles with lacing. In addition, the bridge has angle outriggers. The floor beams and stringers are I-beams. The abutments and cutwater pier are concrete. The bridge is well-preserved, and has not been significantly altered. The lower panel points and floor beam hangers have been repaired with bolts. A modern beam guide rail has been added.

Historical and Technological Significance: The Opie Road Bridge is one of the least altered of over 15 pony trusses remaining in the county from between ca.1900 and 1940. While this is the example that is a riveted Pratt pony truss bridge, it is a late example of riveted pony truss bridge technology, and it exhibits no unusual or noteworthy construction details. The Pratt truss bridge type was patented in 1844 by Thomas and Caleb Pratt of Boston, but did not gain popularity until the last half of the 19th century when it became one of the most common American truss types. Many engineers favored the Pratt truss type because of its easily determined structural action, simplicity and economy of metal. Others, like the opinionated J. A. L. Waddell, recommended its use for thru trusses, but did not recommend its use for pony trusses because of the lack of upper lateral support of the top chord. The perfection of riveted field connections brought the ascendancy of the Warren truss for pony truss spans after the turn of the century, and they are much more common than 20th century riveted Pratt trusses. This span is technologically significant because of it is an uncommon example of a rivet connect Pratt pony truss span. It is also well preserved (criterion C). No local records have been located to determine the builder or engineer for the Opie Road Bridge.

Boundary Description and Justification: The bridge is evaluated as individually significant. The boundary is limited to the span itself, including the substructure.

Discussion of Surrounding Area

The narrow two-lane bridge spans a wide section of the river in the western part of the county. The area is rural with fields, pastures, and a farmhouse (c. 1820) to the west. A housing development (c. 1990) is being built to the east, but out of sight of the bridge.

Bridge Considered Historic By Survey: Yes