The Alton Junction, more commonly known as the 21st Street Crossing, is a historically significant rail location in Chicago, Illinois.
The junction can be found just east of Canal Street and north of Cermak Road near Chicago's Chinatown.
[1] While a significant amount of rail traffic still traverses this interlock every day, it has been greatly reduced from using 26 diamonds to control over 150 trains using the crossing.
The north–south line is the former Pennsylvania Railroad (Pittsburgh, Fort Wayne & Chicago) mainline, which is now owned and operated by Amtrak as the southern gateway to the Union Station complex.
Known as 21st Street tower, its operators handled movements through the busy plant using a US&S Model 14 electro-pneumatic interlocking machine.