CPKC Marais des Cygnes River Bridge

Located south of the small town of Amoret along the Missouri/Kansas border, this unique through truss bridge carries the CPKC mainline across the Marais des Cygnes River. The previous bridge at this location was either a wooden truss or a light iron truss. After KCS acquired the line, significant upgrades were made to the route, and this bridge would be constructed in 1902. The bridge consists of a 230-foot, 11-panel riveted Whipple through truss, approached by a 70-foot through plate girder span on either end. The entire bridge is set onto concrete substructures. The truss utilizes V-laced members, heavy endposts and a unique X-frame/lattice variant portal. The through girders are typical of KCS spans, utilizing round tapered edges and a shallow floor. A missing plaque indicates this bridge was fabricated by the American Bridge Company, which constructed a number of bridges for the KCS and railroads throughout the United States.

The truss span appears to be one of the most unique railroad truss spans in Missouri, and likely throughout the United States. As engineers sought to find solutions to constructing longer truss spans, several different ideas emerged. Historically, pin-connected Whipple trusses had been used for long truss spans (200+ feet). However, these spans were often constructed of iron, and were too weak to carry 20th Century railroad traffic. The design fell out of favor in by the early 1890s, often replaced with large pin-connected Baltimore or Pennsylvania through trusses. During the 1890s and early 1900s, John Alexander Low Waddell developed a number of different experimental truss designs for the Kansas City, Pittsburgh & Gulf Railroad and the Kansas City Southern Railway. Waddell wrote in this book De Pontibus that "The best modern practice in bridge engineering does not countenance the building of structures having more than a single system of cancellation, except in lateral systems where the resulting ambiguity of stress distribution is of minor importance. Waddell further states of Whipple trusses "there is no longer any excuse for its use, because it has been ousted from the position it used to hold by the Petit (Pennsylvania) truss, which excels it in every particular, including appearance, economy of material and mathematical correctness." Waddell also preferred pinned connections, although it is apparent he viewed riveted connections favorably by the 20th Century.

It is believed this bridge was constructed as an experimental span. This particular span utilized the Whipple design, with heavy members and riveted connections. It is unknown why Waddell chose to construct a Whipple truss. It is possible that the KCS requested riveted truss spans, and there was no suitable alternative design for a span of this length. As of 2024, there is no evidence that any other Whipple through truss constructed for road or railroad use utilized riveted connections. While strong, the Whipple truss uses far more material than a Parker, Baltimore or Pennsylvania span, which could span a similar distance. A plaque affixed to the southeast endpost indicates that the span was designed by Waddell & Hedrick of Kansas City, a firm which appears to have been the primary bridge engineer for the KCS.

No other spans of this design were known to have been constructed. By the time this span was built, the Warren design had become the standard for many railroads, offering the benefits of riveted connections, heavier members and greater span lengths as compared to traditional Pratt spans. In addition, the KCS began using riveted Pratt spans for spans in the 200-foot range, and riveted Parker spans soon would be used for larger spans. Because this is such a unique truss span, the author hopes that this span can be preserved, either for railroad use or for another use. The future of this bridge is uncertain, as traffic is projected to increase on this line. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked this bridge as being nationally significant, due to the one-of-a-kind design of the truss. Additional research into the design, reasoning and possible other bridges is ongoing.