From 1958 until 2006, the CTA's most significant non revenue segment was the Paulina Connector. This segment had remained in existence, as the only connection between the Blue Line and the rest of the system, enabling transferring of cars and work trains. This segment previously extended further north of Lake Street to Milwaukee Avenue, connecting with the present elevated segment of the Blue Line northwest to O'Hare Airport. Cut back to Lake Street in 1951, after opening of the Dearborn Subway.
Map to left shows rapid transit routes as they existed prior to 1953. All lines shown were conventional elevated lines. The former Metropolitan West Side Elevated Railroad lines are shown in blue. Main line operated west from the Loop, and continued directly west as the Garfield Park Line. Marshfield Ave. was the main junction on the line, with lines turning south to the Douglas Branch, or turning north to the Logan Square and Humboldt Park lines. One mile north of Marshfield Ave., the line north pased over the Lake Street Line at a higher level, with a station there known as Lake Transfer. The Lake Street Line is shown in green.
Map at center shows routes after the 1958 opening of the Congress Line, operating in the Eisenhower Expressway median strip, below street level, and shown with wider lines. The Garfield Park elevated line was demolished to clear the way for the expressway. At Loomis Jct., the main tracks would separate, while a ramp between the main tracks would connect the median strip line with the Douglas elevated line. The Douglas Line would then turn south, connecting with the Paulina Connector at Harrison Jct. The Paulina Connector is shown in black, and continued north to Paulina Jct., joining the Lake Street Green Line there.
Map to right shows routes after the 2006 introduction of the Pink Line. The connecting ramp is shown in black, and after introduction of the Pink Line would remain in use for certain rush hour Blue Line trains, which would continue over the older routing for two more years.
Cermak Jct. to Federal Jct. - modern elevated structure. Connects the Dan Ryan Red Line with the Midway Orange Line. This provided the Dan Ryan Line with its original access into the Loop, via the elevated. Dan Ryan trains at present will occasionally be diverted via the elevated route for work projects in the State Street Subway.
17th Street Jct. to 13th Street Jct. - connection from elevated to subway. Original connection from south side elevated line to State Street Subway.
Map to left shows rapid transit routes as they existed prior to 1993. The Dan Ryan Line, shown in green, was routed through with the Lake Street Line via the Loop elevated. And the original South Side elevated line, shown in red, operated through to Howard Street via the State Subway. The State Street Subway was opened in 1943, and the Dan Ryan Line was opened in 1969. Prior to 1943, all South Side elevated trains continued over the elevated route into the Loop.
Subway portions are shown with wider lines, other portions are elevated. At 17th Street Junction there are 4 tracks. From 1969 to 1993, Dan Ryan trains used the outside tracks, while the South Side elevated trains used the inside tracks immediately south of the ramp down to the State Street Subway. The northbound track from the Dan Ryan Line would use a flyover to pass over the South Side elevated tracks.
Map to right shows routes effective February 21, 1993, when the two south side lines "traded places". The Orange Line was opened on October 31, 1993, and passes over the new Red Line connection to the State Street Subway. The two non revenue segments of track are shown in black. At 17th Street Jct., Orange Line trains presently use straight routes on the outside tracks, while Green Line trains now pass through diverging crossovers. The 1993 changes nevertheless return the South Side elevated trains to their original elevated route into the Loop.