McKnight Road Overpass

Located on the north side of Chaska, this bridge is the only original overpass remaining along the Minnesota portion of the former Milwaukee Road mainline between Minneapolis and Aberdeen. Often, when railroads were reconstructing mainlines with new bridges and grade separations, old railroad spans were used for the roadway overpasses. Iron and steel girders and trusses would be reused and rebuilt and installed for wagon use. While most of these overpasses made it into the automobile era, very few continue to exist today. Reusing old steel and iron bridge spans was a common and cost effective method for railroads to build bridges. These light railroad spans could feasibly be reconstructed with wood or other cheaper material, and did not require significant amounts of costly steel or concrete. Oftentimes, the bridge spans reused for overpasses were lighter than spans reused for railroad use.

This particular bridge was originally built as part of a 6 span single track deck plate girder bridge across the Rock River at Bridge #C-80 near Watertown, Wisconsin. When that bridge was upgraded in 1910, the spans were reused elsewhere. One span was reused at Bridge #U-762 across the Fox River at Appleton, Wisconsin. Another was reused as part of a temporary bridge across the Des Moines River at Bridge #Z-1154 near Madrid, Iowa. After the permanent bridge at Madrid was completed in 1913, the girder was rebuilt at the Tomah bridge shop and reused here.

When the bridge was rebuilt, the original bracing was cut out, and the bridge converted from a deck girder to a through girder. The structure was widened to 22 feet 3 inches, and altered into a 35-degree skew. The floor was rebuilt with new hangers, floor beams and stringers. A wooden plank deck was placed on the bridge, which would later have an asphalt surface paved over it. The girder span was set onto two concrete frame piers, a design commonly used by the Milwaukee Road during the early 1910s. The bridge would also be approached with 3 wooden pile trestle spans on either end, which sit on timber pile substructures. An unknown contractor fabricated the girder span, and it is unknown if the reconstruction was completed by railroad forces or by an unknown contractor. Construction of the concrete was completed by Milwaukee Road forces. Alterations such as this were common for spans reused for roadway use, and many of these alterations were completed using timber material. After C.F. Loweth took over the Milwaukee Road in the early 20th Century, the railroad became an innovator of concrete bridge design. Numerous examples of similar concrete frame piers were constructed along the Milwaukee Road.

While girder spans were commonly used for railroad bridges, the technology was still emerging in the early 1880s. The Milwaukee Road started using iron girders sometime in the late 1870s, and this span represents a reconstructed version of an early girder structure. Since the initial construction, the bridge has had few alterations. It is likely that the timber components of this bridge were replaced at some point, although no rehabilitation date can be found. The bridge was closed to traffic in 2008, after an inspection found deficiencies with the bridge. The City of Chaska plans to replace the bridge at some point, although little development on McKnight Road north of this bridge has delayed the replacement of this bridge. The author has rated the bridge as being regionally significant, due to the old age and unique reuse of a railroad span. This bridge appears to be the oldest known bridge in Carver County. Audubon Road and Eden Prairie Road also used this type of overpass when the railroad was relocated and reconstructed in 1913, although both have since been replaced.