CHICAGO - MARCH 31: City of Chicago bridge mechanic Jim Hoffman talks on his radio at the semi-up Dearborn Street double-leaf trunnion bascule bridge over the Chicago River, built in 1963, during a bridge maintenance run March 31, 2006 in Chicago, Illinois. The Chicago River may have seen its first bridge in 1832 at Kinzie Street, a small bridge of wood for foot-traffic only. Two years later the first bridge to accommodate vehicles, a drawbridge, was built at Dearborn Street. The City of Chicago currently maintains 52 bridges, of which 37 are movable, spanning various parts of the Chicago River from the downtown area through the North and South branches, not including numerous railroad bridges. With all its tributaries from its furthest north to furthest south points, the Chicago River runs for 156 miles. Some of the current movable bridge types in the city range from the double and single-leaf trunnion bascule bridge, or "Chicago-type" bascule and the Strauss heel-type trunnion bascule railroad bridge to the city's last double-leaf Scherzer rolling lift bridge at Cermak Road. The first trunnion bascule bridge in Chicago, and the United States, was completed in 1902 and can still be seen and driven over at Cortland Street on the city's near-north side. (Photo by Tim Boyle/Getty Images)