Aerial Lift Bridge

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The Aerial Lift Bridge is a landmark in the port city of Duluth, Minnesota. The span began life in 1905 as the United States' first transporter bridge. In 1929-30, the span was converted to a vertical lift bridge and still operates today.

The new design, which closely resembles the 1892 concept, is attributed to C.A.P. Turner. Reconstruction began in 1929.

In order to ensure that tall ships could still pass under the bridge, the top span had to be raised to accommodate the new deck when raised. The support columns on either side were also modified so that they could hold new counterweights to balance the weight of the lifting portion. The new bridge first lifted for a vessel on March 29, 1930.

The bridge can be raised to its full height of 135 feet in about a minute, and is raised about 5,000 times per year. The span is about 390 feet (120 meters).

As ships pass, there is a customary horn-blowing sequence that is copied back. The bridge's "horn" is actually made up of two Westinghouse Airbrake locomotive horns. Long-short-long-short means to raise the bridge, and Long-short-short is a friendly salute.