St. Charles Air Line
The St. Charles Air Line is an interconnection between the BNSF, UP and CN railroads that runs through the South Loop. It may be most notable as the aerial route taken by Amtrak trains from the south and east as they enter into Union Station.
A twin single-leaf Strauss Trunnion bascule railroad bridges carries the Air Line over the South Branch of the Chicago River. The 186-foot northern span was built in 1930 for the Baltimore and Ohio Railroad to lead to their (now demolished) Chicago terminal. Since it no longer leads anywhere, it is locked open. The southern St. Charles Air Line Bridge is a 220-foot span was originally built in 1919 but was shortened and re-erected in 1930 when the South Branch was straightened. (tacotron.com, BridgeHunter.com).