Iron Triangles and River Crossings: The Truss Bridges of Central Jersey

There is a distinct, romantic rhythm to traveling over a narrow, one-lane truss bridge—the low rumble of tires on a timber deck and the rhythmic flash of steel beams passing by. Popularized in the late 1800s, these “iron triangles” were once the backbone of New Jersey’s infrastructure. While many have been replaced by modern concrete spans, the rural landscapes of Somerset and Mercer Counties remain a sanctuary for these historic engineering marvels.

From Revolutionary War routes to “lens-shaped” rarities, these bridges are more than just river crossings; they are modular pieces of American history.

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The Anatomy of a Truss

Truss bridges gained popularity because they were the “IKEA furniture” of the 19th century: inexpensive, easy to fabricate in a factory, and simple to assemble on-site. By arranging iron or steel “members” in triangular patterns, engineers created structures that were incredibly strong yet relatively light.

Know Your Trusses:

• Pratt Truss: Identifiable by its “V” shape, designed in 1844.
• Warren Truss: Uses equilateral triangles; one of the most common designs.
• Lenticular Truss: A rare “lens-shaped” bridge formed by opposing arches.
• Pony vs. Through: A Pony Truss is low enough that you can see over the sides; a Through Truss features cross-bracing over the roadway, creating a “tunnel” effect.

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Mercer County: Bridges of the Revolution

Mercer County’s relationship with the Delaware River has made it a gallery of historic spans, many of which sit directly on the path of General Washington’s 1776 march.

At the very spot where Washington crossed the icy Delaware, a six-span Warren through truss now stands. Built in 1904, it utilizes stone piers that date back to the 1830s. At just 15 feet wide, crossing it in a modern SUV against oncoming traffic feels like a feat of precision engineering.

The Jackson Street Bridge (1888)

Located in the heart of Trenton’s Mill Hill Park, this Pratt through truss was fabricated locally by the New Jersey Steel and Iron Company. Once a busy thoroughfare for brick row homes and mills, it was saved during urban renewal efforts in the late 20th century and now serves as a pedestrian centerpiece for the park.

The Jacob’s Creek Controversy

Perhaps the most famous recent bridge story involves the Jacob’s Creek Bridge. Built in 1882, it sat on “Washington’s Victory Trail.” Despite a massive grassroots effort to save it in situ, the bridge was dismantled in 2011. In a win for preservationists, however, the bridge is slated for reconstruction at Howell Living History Farm, and its modern replacement was designed to respect the historic aesthetic of the valley.

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Somerset County: Architectural Rarities

Somerset County is home to some of the most visually stunning and unique truss bridges in the tri-state area.

The Neshanic Station Lenticular (1896)

Spanning the south branch of the Raritan River is a true “unicorn” of engineering: a Lenticular Truss. Built by the Berlin Iron Bridge Company, its distinctive lens shape makes it one of the most beautiful bridges in New Jersey. Look closely at the original railings—they feature small, cast-iron flower designs, a Victorian touch on a heavy industrial structure.

The “Hybrid” at River Road

In Branchburg, the Opie/River Road Bridge offers a look at “compromise preservation.” When the original 1921 bridge needed to be widened in 2005, Somerset County saved the original truss members and bolted them onto a new, wider concrete deck. While it lost its “one-lane” charm, it serves as an interesting hybrid of 1920s steel and 21st-century safety.

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If You Visit

Truss bridges are best experienced on a slow Sunday drive. Many of these spans are located near historic villages and parklands.

• Neshanic Station: Park near the lenticular bridge and walk across to see the abandoned 1896 Railroad Bridge just a few hundred yards away.
• Washington Crossing State Park: Walk the cantilevered wooden pedestrian path on the south side of the bridge for a spectacular view of the Delaware.
• Mill Hill Park (Trenton): Follow the paths through the park to stand under the massive ironwork of the Jackson Street Bridge.