CPKC Rock River Bridge (Byron, North)

Located on the east side of Byron, this large through truss bridge carries the former Milwaukee Road mainline across the Rock River. While the Milwaukee Road reached the east bank of the Rock River in 1876, a bridge was not constructed across the river until 1882. The first bridge at this location consisted of five 158-foot, 9-panel, pin-connected Pratt through truss spans, constructed at a heavy skew and supported by stone substructures. A heavy skew was required at this location, due to the angle at which the railroad crossed the river. These spans were fabricated by the Edge Moor Iron Works, and utilized built-up vertical members and a lattice portal. By the late 19th Century, traffic on this line had significantly increased, and the Milwaukee Road began a project to double track this line. Between 1897 and 1898, a new single track bridge would be constructed approximately 90 feet north of the existing bridge, and the old bridge was converted to the eastbound track. This new bridge consisted of five 160-foot, 9-panel, pin-connected Pratt through truss spans, set onto new stone substructures. Similar to the 1882 bridge, the bridge would run at a significant skew, although the outer faces of the bridge were square. One interior endpost of each span utilized a vertical member, giving the structure an unusual appearance. An unknown contractor fabricated the trusses, which also utilized built-up members and a more modern lattice portal.

The bridge retained the split configuration until 1905, when a new bridge would be added to the south side of the 1897 structure. This new bridge would consist of five new pin-connected Pratt through truss spans, which utilized a heavier design than the 1897 structure. The 1897-era stone substructures would be widened with concrete to accommodate the new bridge. Work on the structure was completed in 1905, and the original 1882 bridge removed at that time. All five spans of the 1882 were reused along various branch lines in Iowa, Minnesota and Wisconsin. The 1897 spans were replaced in 1929 with new riveted Warren through trusses, giving the bridge its current configuration. At least three of the 1897 spans are known to have been reused on branch lines. A list of spans reused from the 1882 and 1897 has been provided in the table above.

Currently, the bridge consists of two distinct superstructures, which share abutments and piers. The southern track, constructed in 1905, consists of five 160-foot, 6-panel, pin-connected Pratt through truss spans, set onto concrete substructures. These spans use a standard Milwaukee Road design for the era, including a heavy floor, heavy members, a lattice portal and heel bracing with a star shaped cutout. While this structure mainly uses pinned connections, the connections also utilize heavy riveted gusset plates, typical for Milwaukee Road trusses from this era. Typical for skewed truss spans, the bridge utilizes inclined endposts. The northern track, constructed in 1929, consists of five 160-foot, 9-panel, riveted Warren through truss spans, which reused the stone substructures from the 1897 structure. Unlike the southern track, the outer endposts of this structure are square, while the bridge utilizes alternating vertical interior endposts, similar to the 1897 structure. The northern track structure consists of heavily constructed members, including massive built-up beams and an A-frame portal. Pennsylvania Steel Company fabricated the trusses for the south track, while American Bridge Company fabricated the trusses for the north track. It is believed that the substructures were completed by company forces.

Large scale skewed truss spans like this are relatively uncommon, as railroads preferred to construct crossings to avoid the use of skew spans. More unusual with this bridge is the use of two different skew configurations, which share the same substructures. This, combined with the use of two distinct structures, gives the bridge an unusual configuration. Pratt through truss spans were the most popular truss bridge design for railroad use in the late 19th Century, as the design was simple, durable and economical. This design was superseded by riveted Warren designs by the early 20th Century, which were stronger and also provided a simple structure. Since the 1929 reconstruction, the bridge has seen little alterations. A derailment in the 1970s damaged the east end of the north track, which was repaired with new steel. The tracks were removed from the southern structure in the late 1970s, and it has been unused since. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked this bridge as being regionally significant, due to the unusual design and history. In addition to this structure, three spans from the 1882 bridge and three spans from the 1897 bridge are known to still exist.