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Mill Road Bridge

Mill Road Bridge

Primary Photographer(s): Nathan Holth

Bridge Documented: November 8, 2015

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Facility Carried / Feature Intersected
Mill Road Over Rockaway Creek
Rural: Hunterdon County, New Jersey: United States
Construction Date and Builder / Engineer
By Builder/Contractor: Dover Boiler Works of Dover, New Jersey
Rehabilitation Date
Main Span Length
36.0 Feet (11 Meters)
Structure Length
70.0 Feet (21.3 Meters)
Roadway Width
15 Feet (4.57 Meters)
2 Main Span(s)
Inventory Number

Historic Significance Rating (HSR)
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Bridge Documentation

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

This bridge is an uncommon example of a multi-span pony truss, and even more unusual is how short those spans are, with each at only 35-36 feet in length. The Historic Bridge Inventory suggested that the bridge was built by Dover Boiler Works based on style, and noted some details in support of that. One additional detail in support of this was not noted however. Some of the rivets on the bridge are steeple head type which are rare on bridges but were common on boilers, tanks, and other containers. And as the name implies, this was a speciality of Dover Boiler Works. There are an unusual number of bridges in this region that have steeple head rivets on them. Some of them might also be Dover Boiler Works products, but there also was another company, Tippett and Wood of Phillipsburg, New Jersey that built bridges and could be responsible for some of these. However, that company doesn't appear to have done a lot with bridges after 1900, appearing to focus exclusively on tanks, boilers, water towers, etc.

Information and Findings From New Jersey's Historic Bridge Inventory


The two-span riveted Pratt half hip pony truss bridge is supported on a fieldstone substructure. Each 3-panel span is composed primarily of back-to-back angles with web gussets, which is not an uncommon style. Square-headed bolts hold the floorbeams to the gusset plates. Original pipe railings remain. Minimal changes include concrete toe walls and welded outriggers. The bridge is undocumented, but it one of the few riveted Pratt half hips and is thus a good example of its type.


The bridge carries one lane of a country road over a stream. It is located in a wooded setting surrounded by fields and meadows and a handsome 18th-century house that has been reworked in the Colonial Revival mode. A 1757 mill site (non-extant) is nearby. The picturesque, unspoiled setting contributes to the historic character of the bridge. The bridge has integrity of setting.

Physical Description

The 2-span riveted Pratt half hip bridge is supported on a rubble-coursed fieldstone substructure to which some concrete toe walls have been added. Each approximately 35'-long span is three panels, and the members are composed of angle set back-to-back with the gusset plates at all panel points set between the angles. The detail is not uncommon, and it is a design frequently found on Dover Boiler Works bridges. The pipe railings along the inside of the truss lines are original as are the stamped railing brackets. The floor beams are rolled, and the only apparent alteration to the original design is the addition of outriggers or knee braces to provide lateral stability. Some of the field connections are executed with square-headed bolts. The span is well preserved as is its bucolic setting.

Historical and Technological Significance

The 2-span pony truss bridge is significant because it is a rare and nearly complete example of a riveted, rather than the much more common pin-connected, Pratt half hip bridge. Some of the field connects are done with squareheaded bolts, an early-20th century detail that marks the transition from the pin connection to the field rivet connections. Square-headed bolt field connections are not common, but they chronicle the evolution of metal-to-metal connections. Although undocumented in the county engineer's records as to date of construction and fabricator, stylistically the well-preserved span dates to the first decade of the 20th century. It bears design similarities to documented examples of the Dover Boiler Works of Dover, NJ, and it may well be their bridge. The company was active in Hunterdon County during the first two decades of this century according to the Freeholders Minutes. In addition to being a well-preserved example of the early-20th century bridge technology that combines a popular late-19th century pinconnected truss type with more advanced riveted and bolted connections, the bridge enjoys integrity of setting. Located in a county noted for its picturesque agrarian areas and working farms, the span is well sited in an agricultural area that retains its historic rural character. The setting contributes to the historic significance of the bridge.

Boundary Description and Justification

The bridge is located in a well preserved rural setting. While the span is individually significant, it would also be a contributing recourse should the area be evaluated as a rural historic district. The nearby farmhouse and related farm were not evaluated for National Register eligibility as part of this study.


Hunterdon County Engineer. Bridge File: R 24

Bridge Considered Historic By Survey: Yes


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2021 National Bridge Inventory: View listed bridges within 0.5 miles (0.8 kilometers) of this bridge.

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