Lemont Railroad Bridge

Located in Lemont, this unique swing bridge carries the former Santa Fe over the Chicago Sanitatry & Ship Canal. During the late 19th Century, the City of Chicago was rapidly growing, and a solution was required to protect water supplies and create an effective wastewater disposal system. A large canal was designed, which would reverse the flow of the Chicago River and drain outwards from Chicago, ending in the Des Plaines River near Joliet. In addition to improving the wastewater system, the canal allowed larger ships to travel between Lake Michigan and the Mississippi River, via the Illinois River. A number of swing bridges would be required to carry railroads and roadways over the canal.

Construction began on the canal in the mid-1890s, and bridges were constructed during the late 1890s. This structure was constructed in 1898 by the Keystone Bridge Company and MacArthur Brothers Company. The bridge consists of a 398-foot counterbalanced (bobtail) Pratt through truss swing span, set onto stone substructures. The bridge utilizes pinned connections, and consists of a 259-foot, 9-panel south arm and a 139-foot, 4-panel north arm. The two arms are joined by a tower over a center pivot pier, which is constructed of a short section of Bedford, Indiana granite set directly onto native bedrock. The structure contains laced members, a heavy floor and a lattice portal. The bridge was constructed for two tracks, and both continue to be used. The counterweight of the structure is located underneath the north arm, and consists of a concrete slab weighing 429 tons. The entire structure uses 1,158 tons of steel.

Counterbalanced swing spans are a very uncommon design, as they required a degree of precision to construct. This structure utilized a counterbalanced design, as there was not enough room for a wider canal with a pier in the center. Another Santa Fe swing bridge over the canal near Harlem Avenue uses a more traditional design, with two identical trusses joined by a tower. Only a handful of counterbalanced spans are known to exist in the United States, including two others across the North Branch of the Chicago River. Overall, the bridge appears to be in fair to good condition, and is well maintained. The swing span no longer turns, as the rollers and gears at the ends have been removed and timber cribbing braces the bridge from lateral movement. The author has ranked this bridge as being highly significant, due to the unusual design.