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Mine Road Bridge

Mine Road Bridge

Primary Photographer(s): Nathan Holth

Bridge Documented: November 7 and 8, 2015

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Facility Carried / Feature Intersected
Mine Road Over Stony Brook
Rural: Mercer County, New Jersey: United States
Construction Date and Builder / Engineer
1885 By Builder/Contractor: King Bridge Company of Cleveland, Ohio
Rehabilitation Date
Main Span Length
101.0 Feet (30.8 Meters)
Structure Length
102.0 Feet (31.1 Meters)
Roadway Width
16.7 Feet (5.09 Meters)
1 Main Span(s)
Inventory Number

Historic Significance Rating (HSR)
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Bridge Documentation

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This is an excellent example of a Pratt truss by the notable King Bridge Company. It retains good historic integrity, and follows the typical detailing of its builder including plaques.

Information and Findings From New Jersey's Historic Bridge Inventory


One of two well-preserved King Iron Bridge Co. pin-connected Pratt thru trusses in Mercer County, the Mine Road bridge is three years later than Bear Tavern Road (1100060), but is nevertheless an important example of its type. Supported on unaltered ashlar abutments, the 5-panel bridge has few visible repairs. The floor beams may not be original. It is one of four thru truss bridges in the county and ranks as the second oldest and one of the least altered.


On a rural two-lane road, the one-lane bridge crosses a small stream. The bridge enjoys integrity of setting in a rural area dominated by working farms. It is located in the sparsely developed northwestern portion of the county east of busy NJ 31.

Physical Description

The seven panel half-hip pin-connected Pratt thru truss with a steel grate deck installed in 1976 has true hangers that twist 90 degrees out of phase and then pick up the end floor beams. The bearings rest on ashlar abutments. The inclined end posts and upper chord are built-up members composed of shallow channels with a face plate. The same dimension channels are used for the laced verticals. Diagonals (of bar stock with loop-forged eyes) and counters (rods) are fitted with turnbuckles for tuning the bridge, and the bottom chord is die-forged eyebars. The originality of the rolled I beam floor beams is not known, but it is believed that they are not original. They are cut back in section for the suspenders and large square nuts that do appear to be original. The floor beams are fitted with the original brackets for the lateral bracing. The portal struts have a lattice bracing, as does the sway bracing, and each end carries a King Iron Bridge and Manufacturing Co. plaque. The lateral bracing is connected to a crimped bracket that connects at the upper panel point pins. A few welded repairs to the verticals at the panel points are visible, but otherwise the bridge is very well preserved. The modern beam guide rail is attached to the verticals by bolts.

Historical and Technological Significance

The well-preserved 102'-long pin-connected thru truss by the King Iron Bridge and Manufacturing Company of Cleveland, Ohio was erected in 1885, according to its plaque, and is one of two well preserved King thru trusses from the 1880s in Mercer County. The Mine Road bridge, the longer, heavier, and newer of the two, as well as its counterpart on Bear Tavern Road (1100060), are of statewide importance as early examples of a historic bridge type. They are also examples of bridges fabricated by one of the largest and most successful late-19th century manufacturers. The two Mercer County bridges are believed to be the only documented King Iron Bridge and Manufacturing Company in the state. Technologically they reflect early metal truss bridge construction details, such as the true floor beam hangers, the lateral bracing connections, and the prong-like floor beam connectors at the verticals. The bridge is an early and very well preserved example of its type. The King Iron Bridge and Manufacturing Company was established by Zenas King in Cleveland about 1860. Learning the bridge selling business in the 1850s as a salesman representing the Moseley Bridge Company (a patented tubular bowstring), King patented his own tubular bowsting bridge that was to be the company's chief product through the 1870s, and he successfully marketed it nationally through a network of regional representatives. He published catalogues in 1875 and 1884 as well as annual reports. As the market moved away from the light bowstring truss about 1880, he diversified his product line to include the what was becoming standard thru and pony trusses. The King company was one of the largest and most prolific bridge fabricating firms in the country yet only approximately half a dozen documented examples of the firm's work survive in New Jersey. While the company remained an active, viable concern for about a decade after the founder's death in 1892, it was not a regional force in this century. The King Iron Bridge and Manufacturing Company, known as the King Bridge Company after 1892, represents, in addition to period engineering and technology, the manner in which iron and early steel bridges were marketed in this country. The fabricator served as both engineer and builder. That practice was to disappear with the rise of the consulting engineer and the professionally trained county engineer in the early years of this century.


Simmons, David A. "Bridge Building on a National Scale: The King Iron Bridge and Manufacturing Company." The Journal of the Society for Industrial Archaeology. Vol. 15, No. 2, 1989. Mercer County Engineers Office. Transfer File 230.3.

Bridge Considered Historic By Survey: Yes


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Maps and Links: Mine Road Bridge

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