Chicago was a late comer to having subways, although the subject was widely discussed no sooner than the Loop elevated was in operation. In 1937 the City and the federal Works Progress Administration hammered out an agreement resulting in the City's Initial System of Subways. Chicago had asked for a four-track subway beneath State St. and Chicago Ave. connecting with the north and south side elevateds and two east-west streetcar subways. The Feds countered with a two-track State St. subway that went further north under Division St. and Clybourn Ave. that eliminated many curves on the north side 'L'. The Feds said NO to the streetcar subways, but offered instead two options: a subway under Dearborn St. turning under Lake St. and extending west to about Racine Ave, connected with the elevated there and also suggesting that the City connect the Lake St. elevated with the Logan Square/Humbolt Park branch at Paulina Ave.
The second option did not connect to the Lake St. 'L' but turned northwest under Milwaukee Ave. and made the connection north of Division St. A provision for a future Lake St. 'L' connction was built into the curve underneath Milwaukee. The junction would be a "flying junction" as the northbound track is lower than the southbound track, in fact this is the lowest point in the Chicago subway system. Over the decades, several options to use the junction have appeared but none was enacted.
A junction/connection was also provided at the south end of the State St. subway which was expected to eventually connect with an Archer Ave. subway, but the Midway line evolved and the connection ultimately connected with teh Ryan median Red line.