Aerial Lift Bridge

The Aerial Lift Bridge (earlier known as the Aerial Bridge or Aerial Ferry Bridge) is a major landmark in the port city of Duluth, Minnesota. The span began life as an extremely rare transporter bridge — the first of just two such bridges ever constructed in the United States. Originally built in 1905, the bridge was upgraded in 1929–30 to a vertical lift bridge, which is rather uncommon, (although there are six such bridges along Ontario's Welland Canal), and continues to operate today. The bridge was added to the National Register of Historic Places on May 22, 1973. A maritime museum maintained by the United States Army Corps of Engineers exists near the site of the bridge.

• http://en.wikipedia.org/wiki/Aerial Lift Bridge