Historic Bridge Foundation

Most people are familiar with steel truss bridges, but few know about the K-truss, one of the rarest truss types in America. Named for the letter-shaped web of steel in each panel, the K-truss was developed in the 1920s as a way to handle heavy loads with fewer materials. Only a handful of states ever embraced it—chiefly Louisiana, Oklahoma, and Tennessee—and today, very few examples survive. Louisiana, however, is home to two of the most impressive K-truss bridges ever built: the Long–Allen Bridge in Morgan City and the Texas Street Bridge in Shreveport.
Completed in 1933, the Morgan City Long–Allen Bridge (originally US 90, now LA 182) is an extraordinary achievement. Its three massive K-truss spans each measure 607 feet long. To put that in perspective, most truss bridges rarely exceed 500 feet per span. Even more impressive, these are simple spans—each span rests only on its end piers, unlike cantilever or continuous spans that transfer loads across multiple supports. Achieving over 600 feet with this straightforward design was virtually unheard of, making Morgan City’s bridge a national record-holder.
The bridge is a subtype called a K-Parker truss, a polygonal truss with the distinctive K-pattern bracing. Beyond its structural achievement, the bridge is visually striking: long approaches rise to meet three soaring steel spans that stretch boldly across the Atchafalaya River. When it opened, it completed an essential link in the Old Spanish Trail highway, replacing ferries and connecting communities across southern Louisiana.
Construction itself was remarkable. Each enormous 1,400-ton truss was assembled on shore and floated into place on barges—an early form of accelerated bridge construction. Today, more than 90 years later, the bridge remains in service. Preservationists consider it one of Louisiana’s most beautiful and significant historic bridges, a true landmark that reflects the bold engineering spirit of its time.
Also built in 1933, the Texas Street Bridge in Shreveport (sometimes confusingly also called the Long–Allen Bridge) takes the K-truss in a very different direction. Rather than simple spans, this bridge uses a cantilever design—one of the only cantilever bridges in the U.S. to use a K-truss. Its main suspended span stretches 520 feet, anchored by cantilever arms and side spans for a total length of nearly 3,000 feet.
What makes the Texas Street Bridge stand out is not just its rare K-truss cantilever structure, but its graceful appearance. Traditional cantilever trusses have tall, pointy towers above their piers. This bridge, however, was designed with a smooth arching top chord, giving the whole structure a flowing curve instead of sharp peaks. It was one of the earliest experiments in making big steel bridges look elegant as well as strong. A few years later, other famous bridges like the Blue Water Bridge in Michigan and the Rainbow Bridge in Texas would adopt similar arch-like profiles (though not with K-trusses).
The Texas Street Bridge remains an icon of Shreveport’s skyline. In recent decades it has been outfitted with decorative lighting, making it both a practical crossing and a nighttime landmark. After a major rehabilitation in 2019–2020, it continues to serve traffic across the Red River while also acting as a symbol of the city’s history and growth.
Together, the Morgan City and Shreveport bridges represent Louisiana’s unique place in American engineering history. The Morgan City Bridge pushed the limits of simple span design, achieving a record length that still commands respect. The Shreveport bridge showed how K-trusses could be adapted to a cantilever system, and did so with a rare grace and elegance that set a trend for later bridges.
Few states built K-truss bridges at all, and even fewer still have examples standing. Louisiana’s pair are not only survivors—they are among the most significant K-truss bridges in the nation. They remind us of an era when engineers were experimenting boldly, solving practical challenges with creativity, and leaving behind landmarks that continue to inspire.
Preserving these bridges means more than just maintaining old steel. It means honoring a chapter of innovation in America’s infrastructure, keeping alive the stories of the communities they connected, and celebrating the artistry hidden within structural engineering.