CN Dearborn Street Bridge (Near South Side)

Located north of 16th Street, this through and deck plate girder bridge once carried the St. Charles Air Line over Dearborn Street. In the late 19th Century, the numerous grade crossings throughout the City of Chicago posed a serious hazard to the general public. Overpasses, which carried roads over the railroads, were expensive and detrimental to the surrounding properties. In addition, the web of railroads intersecting near 16th Street proved difficult to elevate. By the late 1890s, the railroads began to work with the city to elevate segments of track through the city, placing subways at street crossings. The City and railroads reached an agreement to grade separate the large railroad junction near 16th Street, as well as elevate the St. Charles Air Line and other railroads. Work began on the project in 1898, starting with the construction of a temporary trestle. Retaining walls were constructed through the summer of 1898, and steel bridges were placed in the winter of 1899. Work on the project was substantially complete by June of 1899. Typical of early track elevation projects in Chicago, the retaining walls are constructed of stone. The retaining walls were constructed in 100-foot sections, to provide expansion joints and reduce settling concerns.

The bridge at Dearborn Street consisted of a 38-foot through plate girder span, approached by a 16-foot deck plate girder span on either side. The spans were set onto steel bents and stone abutments, and the bridge was constructed for four tracks. The floors of the girder spans consisted of parallel floorbeams, topped with sheet metal to form a closed deck. The bents of the bridge were constructed of steel columns, connected by riveted steel plates. Detroit Bridge & Iron Works received the contract for the superstructure, and J.S. Patterson Construction Company constructed the substructures. Stone for the abutments and retaining walls was quarried at Williamsport, Indiana and Berea, Ohio. This type of structure was initially popular for grade separations in Chicago, but fell out of favor as trough floor spans and concrete spans became more economical. The metal floor of this design of bridge was susceptible to pooling water, which would cause corrosion to the steel. In addition, the through girder design limited horizontal clearances on the bridge. The bridge would be replaced in 2020. The bridge was in poor condition at the time of replacement, with severe deterioration throughout the structure. Additional bents had been added to the piers, and the floor had significant holes in it. Through the 21st Century, the bridge carried only two tracks and had a speed restriction. The author has ranked the bridge as being locally significant, due to the common design.