Rockford Railroad Crossing (East)

Located in Rockford, this unique helicoidal skew stone arch bridge once carried the Chicago & North Western Railway over the riverfront industrial trackage owned by the Chicago, Burlington & Quincy Railroad (CB&Q). In 1875, the Chicago & Iowa Railroad (C&I) opened a branch line from Flagg Center to Rockford. The C&I was operated under lease by the CB&Q, and this rail line provided the CB&Q with access to Rockford. In the early 1880s, the C&I desired to construct industrial trackage along the east bank of the Rock River, north of the C&NW tracks. To facilitate this, the C&I contracted with H.T. Smith to construct a crossing of the C&I track immediately east of the Rock River bridge. Smith was a prominent stonemason in Rockford, had he had worked on a number of buildings and bridges in the area, including the piers for the adjacent C&I Rock River bridge some years earlier. The bridge was constructed in December of 1882, using stone quarried at the C&NW quarries in Batavia, Illinois.

Currently, the bridge consists of a 15-foot helicoidal skew stone arch span, set onto stone substructures. A traditional arch bridge could not be used due to the angle at which the C&I crossed underneath. The total length of the structure is 22 feet, which is very narrow for a stone arch bridge. Helicoidal stone arches are a rare example of a skewed stone arch. On a typical stone arch bridge, courses of stone are laid parallel to the abutments, giving the structure a rectangular shape. However, skew arches are required to be constructed in a parallelogram shape, requiring precise stone cutting and placement. The helicoidal design uses a spiral pattern, which allowed for stones to be cut in a consistent pattern. Stones for the voussoir stones would be cut with curved surfaces, which formed parallel spiral courses. This design was invented by British architect Peter Nicholson in 1828. While requiring a greater level of mathematical calculations in designs, this design allowed for a simpler construction and provided a stronger structure than a ribbed arch.

This bridge is one of only a handful of examples of a helicoidal stone arch in the United States, and one of only three known examples in Illinois. Stone arch bridges were popular with the C&NW, as the railroad had access to plenty of quality stone. This design provided a durable and easy to construct design. It is likely that the C&NW required the C&I to pay for installing a premium stone structure, instead of using timber or iron. Since the original construction, the bridge has remained virtually unchanged. No significant repairs have been made to the structure. Overall, the bridge appears to be in fair to good condition, with only minor deterioration to the stone. The author has ranked the bridge as being highly significant, due to the age and unusual design.