BIBLIOGRAPHY: Hunterdon County Engineer's Office, Bridge card D388. Schmidt, Hubert G. Rural Hunterdon: An Agricultural History. New Brunswick: Rutgers University Press, 1945. PHYSICAL DESCRIPTION: The two-panel, pin-connected slightly skewed Warren pony truss bridge has several unusual features. The top chord is a riveted box member consisting of angles and plate and a continuous cover plate, bent at the inclined end posts. Gusset plates secure the diagonals at the lower panel points. The bottom chord and diagonals are toe-in angles. The vertical member, a modification to the original design made after 1974, consists of two angles with a center separating batten and a central rod which threads through the top chord into a fastening finial. The bottom of the rod is a forged loop that passes around the pin that U hanger for the single flame-cut floor beam. The bridge is supported on random fieldstone abutments with wingwalls. The original medallion and lattice railing remains, but collision damage has buckled the east end post and railing. Concrete scour protection has been added, and a concrete toe wall has been added to the east abutment. Other minor repairs include welded reinforcing plates at the bottom of one inclined end post. HISTORICAL AND TECHNOLOGICAL SIGNIFICANCE: The diminutive pony truss bridge is technologically distinguished because it is a hybrid design variation on a Warren truss that reflects the experimental nature of metal truss bridge design in the 19th century. One of two nearly identical spans built over Plum Brook between 1900 and 1903, the designer is not documented, but it is probable that it was the builder of both spans, J. W. Scott, a fabricator from Flemington. According to Hubert Schmidt, Scott operated a foundry which specialized in the manufacture of iron bridges "during the latter part of the nineteenth century." (Schmidt, 220.) Scott also built two thru-truss bridges at Woodfern in Somerset County (18B0511, 18B0512)[ see http://bridgehunter.com/scripts/bridge/edit.cgi?bridgeid=25551 ]. Like its companion (100D390)[Stone Signpost Road, 300 yards North], the bridge has minor alterations and repairs, but its design integrity and setting have not been compromised. The two bridges are the only documented examples of their design in the state, and while not representing the state of engineering or understanding of sound engineering principles of their day, do represent the variety and idiosyncrasy of bridge designs that characterize the heyday of the metal truss bridge era. Because both bridges are relatively well preserved, both have been evaluated as significant.
The 2004 reconstruction changed this bridge somewhat from how it was described in the county survey document quoted here. The central vertical is now just a single square section steel rod.
I can not say if the "flame cut floor beam" is the same one that was there prior to the 2004 reconstruction, but the modifications to this bridge are extensive enough that it feels like a cheater to serious bridge fans.
Almost every single rivet has been replaced with nuts and bolts, and welding has been added to most plates. The bridge appears to be pin-connected but it isn't; the pin merely holds the humorously large (for such a tiny bridge) single wide flange floor beam in place. Lower chord are angle sections, "toe in". The joists are also quite significant, the abutments new, and the crash barrier is so sturdy that it nearly hides the remains of the turn of the 20th century style lattice railing with it's decorative medallions and ball finials that match the top finial on the top chords. At this point the vertical is just for show and is never under tension or compression. I have strong doubts that the pony truss itself is doing any work, considering how short the bridge is and how significant the joists and the one floor beam. It's effectively become a girder bridge with a truss perched on it for looks.
It is a cute little bridge, and it's a nice find on a quiet wooded country road. And you will rarely ever see one with a "bedknob" perched on top. But the county has modified it so that oblivious drivers can race across it in their big trucks and SUVs without concern. That's the way the world is going unfortunately; it's a fate that is in the cards for most old bridges. Get modernized or get replaced with some soulless concrete slab.