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Jackson Road Bridge

Jackson Road Bridge

Primary Photographer(s): Nathan Holth

Bridge Documented: November 7, 2015

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Key Facts

Location
Rural: Somerset County, New Jersey: United States
Construction Date and Builder / Engineer
1927 By Builder/Contractor: Unknown

Technical Facts

Rehabilitation Date
2008
Main Span Length
57 Feet (17.4 Meters)
Structure Length
62 Feet (18.9 Meters)
Roadway Width
21.3 Feet (6.49 Meters)
Spans
1 Main Span(s)
NBI Number
18E1401

Historic Significance Rating (HSR)
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Bridge Documentation

View Archived National Bridge Inventory Report - Has Additional Details and Evaluation

This is a traditionally composed riveted truss bridge. However, its truss configuration is that of a Warren truss with no vertical members. Because nearly all Warren truss bridges have vertical members, this truss is therefore a rare example of one without verticals.

This bridge is listed in the National Bridge Inventory as a County-Owned, taxpayer funded bridge. Yet the bridge connects a county road (Branch Road) to a road that immediately at the end of the bridge is posted as a private road. Its unclear how such an unusual situation came to be (a public taxpayer funded bridge serving a private driveway) but for this reason it is recommended that visitors to the bridge approach from the west on Branch Road. The bridge itself remains listed as a public, taxpayer funded bridge in the National Bridge Inventory however, so visitors to this bridge should understand that they have a legal right to walk on the bridge deck, even if the road east of the bridge is private.

Information and Findings From New Jersey's Historic Bridge Inventory

 Summary

The skewed rivet-connected 4-panel Warren pony truss bridge is a complete example of its type, but its design is typical of the period. It is composed of channels and plates for the chords, and of angles joined by battens for the diagonals. The Warren is the most common 20thcentury truss type for highway bridges. The newest of the 10 Warren pony truss spans in the county, it is an extremely well preserved example of the historically significant bridge type, and it is thus notable.

Setting/Context

The single-lane bridge spans the river and connects Branch Road on the west bank with a private lane (Jackson Road). The surrounding area is hilly and rural with pastures, wooded lots, and scattered 19th- and 20th-century residences.

Physical Description

The skewed 62'-long riveted Warren pony truss bridge is supported on a concrete substructure. The span is extremely well preserved. The upper chords and inclined end posts are built up box members with channels with cover plate and lacing. The diagonals are toe-down angles with battens, and the lower chords are toe-up angles with battens. Asymmetrical gusset plates are placed on both sides of the lower panel points, and they too are stiffened with a batten plate. The floor beams and stringers are rolled I sections. Lattice railings are still in place on the inside face of the trusses. As complete as the trusses is the rural setting of the bridge, which services and unimproved road.

Historical and Technological Significance

The Warren pony truss bridge on Jackson Road was built in 1927, and it is the latest of the surviving examples of metal truss bridges in the county. While exhibiting no innovative or patented details, the span is technologically and historically significant as a well preserved survivor of the last years of metal truss bridge erection in the area (criterion C). It was apparently designed by County Engineer Oscar Smith, Jr., who succeeded longtime County Engineer Joshua Doughty, and it was built at a time when most county-designed spans were encased stringers. There is no indication that this bridge was moved to Jackson Road from another location. Prior to the widespread acceptance of rolled steel stringer and reinforced concrete arch bridges in the 1910s, the Warren pony truss was the most common early-20th century highway bridge for crossings of less than 100'. The Warren truss bridge type was patented in 1848 by two British engineers, James Warren and Willoughby Monzani. It differed from other trusses in that it did not have a vertical (compression) member and that alternate diagonals slope in opposite directions. Because some of those diagonals are compression members, the design was not well suited for pinned connections. With the perfection of the portable pneumatic equipment in the late-19th century, field riveting was possible, and the simple but rigid Warren truss came to the fore during the 1890s. During the early 20th century, steel Warren trusses appeared in rapidly growing numbers, and were used for both highway and railroad spans. However, by the end of the 1920s. few, if any, metal pony truss highway bridges were being built in New Jersey.

Boundary Description and Justification

The bridge is evaluated as individually distinguished, although its rural setting does offer fine integrity of setting. The significant boundary is limited to the span itself, both the superstructure and substructure.

Sources

Somerset County Engineer: Bridge File: E141. Musti, J. Somerset County New Jersey 1688-1930. Camden, N.J., 1930.

Bridge Considered Historic By Survey: Yes

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Photo Galleries and Videos: Jackson Road Bridge

 
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Maps and Links: Jackson Road Bridge

The road east of this bridge is posted as private, so approach this bridge from the west.

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