6-May-15 – It was a big day for Mayor William “Big Bill” Thompson. The Michigan Avenue Bridge he had strongly supported was opening on his 50th birthday.

The notion of linking the boulevard systems on the north and south sides of the Chicago River to ease congestion was first discussed in the 1890s. At the turn of the century, planning became more focused and the project ultimately became an important part of the 1909 Plan of Chicago. Due to a number of factors, including World War I, construction did not begin until April 1918.

Only the upper deck and two operable bridge houses, which were steel skeletons covered in plywood, were ready for the opening ceremonies on May 14, 1920. The lower deck was completed at the end of 1920, followed by the masonry work on the four bridge houses in 1922. The bas-relief panels that adorn each bridge house were completed in 1928. (Left) Michigan Avenue Bridge in 1927. Image obtained from Chicago History Museum.

While this bridge was a new crossing, it replaced a long-lived center pier swing bridge at Rush Street, just west of Michigan Avenue. Traffic had grown to the point that the old bridge was a major bottleneck on both land and water.

The Michigan Avenue Bridge is the second of four double-deck trunnion bascule bridges built in downtown Chicago. It was unique in two respects. Both decks carried vehicular traffic – six lanes of boulevard traffic on the upper deck and four lanes of commercial traffic on the lower deck.

Hugh E. Young	Thomas G. Pihlfeldt	Edward H. Bennett

The lead designers were engineers Hugh E. Young and Thomas G. Pihlfeldt. Edward H. Bennett was the consulting architect for Chicago Plan Commission and William A. Mulcahy was chief engineer in charge of construction. Great Lakes Dredge and Dock Company of Oak Brook, Illinois, accomplished the substructure and steel erection. American Bridge Company of Downers Grove fabricated the steel.

The trunnion bascule bridge is a balanced horizontal seesaw with unequal arms – the longer arm is the bridge leaf over the river, the shorter arm supports the much larger counterweight on the shore. In the case of the Michigan Avenue Bridge, the leaf weight is approximately 4,100 tons (8.2 million pounds), while the counterweight is around 12,000 tons (24 million pounds). Because it is balanced, only a small amount of external energy is required to raise and lower the bridge. Two 108-horsepower electric motors and a simple gear system generate the power necessary to raise each half of the bridge in about one minute. For comparison, an electric Fiat 500e car weighs 2,980 pounds and is powered by a 111-horsepower motor.

(Right) Gears that raise and lower the DuSable Bridge at Michigan Avenue, located inside McCormick Bridgehouse & Chicago River Museum.

The four neoclassical Beaux-Arts bridge houses and its central location make this the most recognizable – and to many, the most beautiful – of Chicago’s bascules. Functionally, the bridge only needed two bridge houses, in the northwest and southeast corners, for operation. The second pair was added to make an architectural statement about the importance of this crossing as a gateway between the north and south sides of the river.

Different names have been proposed over the life of the iconic bridge. In 1921, the Chicago Historical Society suggested “Marquette-Joliet Bridge.” In 1939, the Fort Dearborn memorial committee offered “Fort Dearborn Bridge.” In 2010, after a decade of effort, Friends of DuSable and the DuSable League convinced the city to rename the bridge “DuSable Bridge” after Jean Baptiste Point du Sable, the first non-native settler in the area. (Left) On July 17, 2010, during filming of Transformers 3, the north half of the bridge is raised and a car at upper right appears to hang over the edge.

Arguably the most dramatic incident in the bridge’s history happened on September 20, 1992, when one of the bridge leaves became a catapult. The bridge was being renovated and during a seemingly routine bridge lift only the two north leaves were raised for sailboats. As the north leaves lowered, the southeast leaf sprang up, sending debris across the upper deck. A 40-ton crane fell through the gap between the bridge and the street and the crane’s 285-pound wrecking ball landed on an occupied car on Lower Wacker Drive. The bridge leaf broke off its trunnions and fell into the pit. Luckily, no one was seriously injured, including the man sitting in his car.

The cause of the accident was a combination of a severely unbalanced bridge leaf and partially disengaged safety locks. This condition allowed the rack and pinion to un-mesh and the leaf rose uncontrolled. The bridge was reopened to traffic on November 25, 1992.

DuSable Bridge is a defining image of Chicago, whether seen in films, television, or news broadcasts. It is one of the most photographed landmarks in the city. In 2010, it was the end point for the Stanley Cup parade. It also serves as the central landmark for the annual St. Patrick’s Day dyeing of the Chicago River and the Magnificent Mile Lights Festival.

(Above) “Opening of Michigan Boulevard Bridge, May 14, 1920, 4 p.m,,” reads the caption of this image from Chicago History Museum.

Other facts about the DuSable Bridge…

• In its first year, the bridge was raised 3,327 times and it was estimated that each lift stopped about 350 vehicles on both levels. Today, the bridge is raised about 50 times each year to allow sailboats to get between Lake Michigan and winter storage.
• What appears to be one large bridge is essentially two smaller bascule bridges side-by-side. The two are tied together to operate as one but can operate independently if needed.
• The outboard sidewalks on the lower deck have only been there since 1972.