Lake Street Bridge

View an article describing the construction of this bridge

Located near the confluence of the North Branch and South Branch of the Chicago River, this iconic double deck bascule bridge carries Lake Street and the CTA Green and Pink Lines over the South Branch Chicago River. The present bascule bridge is the fifth bridge at this location. The first bridge to carry Lake Street across the South Branch Chicago River was a wooden swing bridge, constructed in 1852. This first bridge was constructed by Derastus Harper, and was powered by hand. That bridge would be replaced in 1859 by a similar bridge, constructed by Chapin & Company. A third bridge would be constructed in 1867, and used a combination of wood and iron. This bridge utilized a pony truss design, set onto a stone pier and abutments, and was constructed by Fox & Howard. The 1867 bridge was eventually retrofitted to carry a streetcar line. By 1885, the wooden bridge had become too light for traffic, and constructed began on a new iron bridge. The bridge would be completed in 1886 by Detroit Bridge & Iron Works; set onto new stone substructures. The bridge would be 220 feet long, consisting of a pin-connected Pratt through truss with a curved top chord. Costs of the new bridge were split equally between the City of Chicago and the West Division Street Railroad Company, which operated a streetcar line along Lake Street.

In 1893, the Lake Street Elevated/Chicago & Oak Park Elevated Railroad constructed an elevated railroad over the Lake Street Bridge. As part of the work, the iron swing bridge was strengthened with a third truss line, and an upper deck added to the bridge. Due to the large volume of railroad traffic, this arrangement did not work well for the railroad, as the bridge was required to open and close several times through the course of a day. In addition, the bridge impeded river traffic, due to the location of the center pier. In the late 1890s, the Army Corp of Engineers studied the bridges throughout Chicago to facilitate improvements for river traffic. Swing bridges were identified as being unacceptable to cross the river, due to the navigation constraints. By the early 1910s, planning began for a new bridge to replace the aging swing bridge. Engineer Alexander F. von Babo oversaw the design of a new bascule bridge, which was designed by the City of Chicago Engineering Department. The initial plans were completed in 1912, and contained three tracks. The plan was revised in 1913 to only utilize two tracks. Because of the nature of this bridge, a new bridge would have to be constructed while not interfering with the swing bridge. Bids were opened in September of 1913, but the lowest bid exceeded the estimate of the bridge.

During the early 20th Century, a number of movable bridge designs were patented by engineers, many of whom were based in Chicago. The owners of these patents claimed that a bridge could be constructed for cheaper, using a patented design. A commission of three engineers was selected in October 1913. Included in this group were John Ericson, City Engineer; J.E. Greiner, Consulting Engineer; and William H. Finley; who was selected by the other two members. Various proposals were received by this Commission for bridges which could be constructed without interfering with the existing bridge. A vertical lift design was recommended by the Commission; however, the City Council recommended a double-leaf bascule bridge be constructed due to aesthetics. The proposals were rejected, and revised plans prepared.

The construction of the new bridge would be completed by erecting the two halves of the bascule span in an upright position. Sidewalks were first removed from the old bridge, so a wider channel could be maintained. The street-level approach spans were then removed, and the original abutments left in place temporarily to carry the elevated railway. The deck plate girder viaduct approaches which carried the elevated railroad were then braced with timber bents. As work began on the abutments and tailpits of the new bridge, scrap girders were installed to carry the steel bents of the viaduct. Once the bents were transferred to these girders, the tailpit and abutment could be completed. The substructures were substantially complete by January 1915, and steel began to arrive in February of that year. Throughout the second half of 1915, work on the superstructure progressed. At completion, the swing bridge was opened; the center cut away, and the new bridge lowered into place. The remaining portions of the old bridge were then demolished. Steel for the bridge was fabricated by the American Bridge Company; FitzSimons & Connell Dredge and Dock Company completed the substructures and Ketler-Elliott Erection Company completed the erection of the bridge.

The bridge consists of a double deck Warren through truss bridge, which carries Lake Street on the lower level, and the two elevated railroad tracks on the upper level. Typical of bridges in Chicago, the bridge consists of a double leaf fixed trunnion bascule span, where the two halves of the bridge rotate upon their endpoints. The trusses are spaced at 42 feet apart, and the deck of the bridge is 70 feet wide. The truss measures 245 feet from center to center of the trunnions. Each leaf of the bridge consists of a 123-foot, 8-panel riveted Warren through truss, which are cantilevered from the ends. The ends of the spans consist of a 48-foot carrying truss, and a machinery girder. The ends of the spans are located over a large concrete pit, known as a tailpit. This pit allows the bridge to rotate, and holds the machinery. The carrying trusses carry the entire dead load of the bridge. In addition, the bridge utilizes decorative concrete substructures, and machinery houses are located on the northwest and northeast corners of the bridge. Similar to other lift bridges in Chicago, these machinery houses are constructed of concrete and glass, and add to the aesthetic of the bridge. Members of the trusses are constructed of built up members, which utilize heavy lacing. The roadway floor of the bridge is constructed of an open grate deck, which was often used on city owned lift bridges. When completed, this bridge was the first double deck bascule bridge completed.

Throughout Chicago, this design of bridge was popular for city owned crossings of the Chicago River. The design provided a design that was both functional and aesthetic. Since the initial construction, the bridge has seen a number of modifications. The original deck was replaced after the streetcar line was removed. Other repairs have been made to the bridge over the years, including the reconstruction of the east end elevated railroad approach viaduct, which was partially reconstructed with a pony truss span in the 1980s or 1990s. As of 2024, a significant rehabilitation project has been planned for the bridge. This project will replace deteriorated members and floorbeams of the bridge, as well as give the entire bridge a general rehabilitation. Overall, the bridge appears to be in fair condition, but needs a significant rehabilitation to continue to reliably serve traffic. The author has ranked this bridge as being regionally significant, due to the unique design of the bridge. Despite the large quantity of similar spans in Chicago, relatively few exist on a national scale. In addition, double deck versions of this type of bascule bridge are only found in Chicago. In addition to this bridge, similar double decked bridges are used at Wells Street, Michigan Avenue and Lake Shore Drive.