West Main Street Bridge, Spanning South branch of Raritan River, Clinton, Hunterdon County, NJ

Significance: The Lowthorp Truss Bridge represents an early type of iron truss that dominated bridge construction from the 1850s to the 1870s. Fabricated in 1870 by William and Charles Cowin of Lambertville, New Jersey, the bridge follows the Pratt configuration in the arrangement of its trussing members. It is of composite construction, with all compression members made of cast-iron and all tension members made of wrought-iron. In the Pratt truss, the vertical posts and horizontal upper chord are in compression and are made of cast-iron; the diagonals and bottom chord are in tension and are made of wrought-iron. Cast-iron members and lower chord connections are based on truss bridge patents received by Francis C. Lowthorp of Trenton, New Jersey, during the 1860s and 1870s.

The West Main Street Bridge is one of three existing Cowin-fabricated spans in New Jersey. It is also one of two Cowin bridges that used William Johnson's patented tension adjuster.
Unprocessed Field note material exists for this structure: FN-8
Unprocessed Field note material exists for this structure: N15
Survey number: HAER NJ-19
Building/structure dates: 1870 Initial Construction