Bollman, Wendel

The structure has two segments: an East Channel bridge consisting of four 175-foot spans and three 240-foot spans crossing from Harrisburg to City Island; and a West Channel bridge, consisting of seven 175-foot spans crossing from City Island to Wormleysburg.

With 15 truss spans totaling 2,820 feet, the Walnut Street Bridge is the finest and largest surviving example of the standardized Phoenix wrought-iron truss bridges produced from 1884 to 1923.

The design of the Bollman Truss Bridge-patented in 1852 and one of the first to use iron exclusively in all essential structural elements-was critical in the rapid expansion of American railroads in the 19th century. Replacing wooden bridges, which  were cumbersome to build and vulnerable to decay, the Bollman Truss Bridge could be built relatively quickly and inexpensively, while providing the long-lasting qualities associated with metal. This allowed new rail lines to be built over long distances in a short period of time.