CPKC Rock River Bridge (Afton)

Located southeast of Afton, this through plate girder bridge carries a former Chicago, Milwaukee, St. Paul & Pacific Railroad (Milwaukee Road) line over the Rock River. Little is known about previous bridges at this location. The first bridge at this location may have been a timber truss bridge, constructed when the line was first built. In the early 20th Century, the Milwaukee Road upgraded numerous major bridges throughout the system, replacing outdated timber bridges with new metal and concrete bridges. In 1909, the present bridge was constructed at this location, using secondhand wrought iron deck plate girder spans. Currently, the bridge consists of six 65-foot deck plate girder spans, set onto concrete substructures. While not officially designated as such, the superstructure uses a typical design for type "A4" deck plate girder spans, including two heavy girders and an open deck. These spans were originally fabricated in 1890 for use at Bridge #A-262, which was a double track bridge crossing the Root River near Caledonia, Wisconsin. When that bridge was replaced in 1909, a total of six spans were released for reuse. Instead of scrapping the spans, it was decided to install them at this location, with minimal alterations. The substructures consist of standard diamond shaped piers and abutments with sloped wing walls. An unknown contractor fabricated the superstructure, and labor employed by the Milwaukee Road Bridge & Building Department constructed the substructure. Railroads often reused steel and iron spans, as it provided a cost effective way to upgrade branch line bridges without requiring large amounts of new material. The Milwaukee Road reused spans wherever feasible, oftentimes with significant alterations which were performed in-house. Due to the strength of these spans and their initial construction for heavy mainline use, it appears that no significant alterations were required. Deck plate girder spans were often used by railroads, as they provided a durable and easy to construct design. Since the initial construction, the bridge has seen no major structural alterations, and remains in regular use. Overall, the bridge appears to be in fair to good condition, with the superstructure appearing to retain excellent integrity. The author has ranked this bridge as being moderately significant, due to the age, reuse and use of wrought iron in plate girder spans.