Editing Blue Line (CTA) (section)

== Route ==
{{unreferenced section|date=November 2024}}
{{See also|Logan Square branch}}
{{multiple image
 |align = left
 |direction = vertical
 |width = 210
 |image1 = O'Hare station 2018.jpg
 |alt1 =
 |caption1 = The Blue Line terminal at [[O'Hare International Airport]]
 |image2 = Clark-Lake subway 2.jpg
 |alt2 =
 |caption2 = Clark/Lake station on the Milwaukee–Dearborn subway
 |image3 = Eisenhower Expressway.jpg
 |alt3 =
 |caption3 = The Blue Line tracks in the median of the [[Eisenhower Expressway]]
}}

=== O'Hare branch ===
The '''O'Hare branch''' is the longest section of the Blue Line ({{convert|14.6|mi|km}}) and comprises both the oldest and newest segments of the entire route. The line starts at [[O'Hare International Airport]] in [[O'Hare station|an underground station]] below the airport's main parking garage, with direct pedestrian access to Terminals 1, 2 and 3. The line emerges in the median of the O'Hare main access road ([[Interstate 190 (Illinois)|Interstate 190]]) just northwest of Terminal 5, about a mile (1.6&nbsp;km) west of Mannheim Road.

The line runs in the median of [[Interstate 190 (Illinois)|Interstate 190]] east through [[Rosemont, Illinois|Rosemont]]. The line has a station at River Road in {{cta|Rosemont}}, which is also the location of the northern storage yard and served as a temporary terminal from 1983 to 1984 while the O'Hare station was being completed. The tracks then tunnel beneath the [[Kennedy Expressway]]/[[Northwest Tollway]] interchange near the [[Des Plaines River]].

The line runs in the median of the Kennedy Expressway ([[Interstate 90 in Illinois|Interstate 90]]) until a point southeast of Addison Street, making stops at {{cta|Cumberland}}, {{cta|Harlem|Blue|O'Hare}}, {{cta|Jefferson Park}}, {{cta|Montrose|Blue}}, {{cta|Irving Park|Blue}} and {{cta|Addison|Blue}}. Between Montrose and Irving Park, the line tunnels beneath an express lane exit. South of Addison Street, the line descends into a subway and turns south under Kimball Avenue. The line travels under Kimball Avenue and [[Milwaukee Avenue (Chicago)|Milwaukee Avenues]] through [[Logan Square, Chicago|Logan Square]], making stops at {{cta|Belmont|Blue}} and {{cta|Logan Square|Blue}}.

South of Logan Square, the line emerges above ground onto an elevated structure parallel to Milwaukee Avenue. This section of structure, built in 1895 as part of the Metropolitan Elevated's [[Logan Square branch]], is the oldest portion of the Blue Line, and the sole section of the line on an elevated viaduct. The three stations on this section ({{cta|California|Blue}}, {{cta|Western|Blue|O'Hare}}, and {{cta|Damen|Blue}}) are also the only three stations on the line to use side platforms instead of island platforms.

=== Milwaukee–Dearborn subway ===
{{Main|Milwaukee–Dearborn subway}}
At the intersection of Ashland and Milwaukee Avenues, the Blue Line descends underground, swings over to Milwaukee Avenue, and continues southeast towards downtown under Milwaukee Avenue (with stops at {{cta|Division|Blue}}, {{cta|Chicago|Blue}} and {{cta|Grand|Blue}}). The line then turns east under Lake Street, crossing beneath the [[Chicago River]], and makes a stop at {{cta|Clark/Lake}}, where in-system transfers are provided to 'L' trains on the Loop.

East of Clark/Lake, the tracks swing south under Dearborn Street, with a continuous platform similar to the continuous platform used in the adjacent [[State Street subway]], with stops at {{cta|Washington|Blue}}, {{cta|Monroe|Blue}}, and {{cta|Jackson|Blue}}.

South of Jackson, the line turns west under [[Ida B. Wells Drive]] (with stops at {{cta|LaSalle}} and {{cta|Clinton|Blue}}, which is two blocks south of [[Chicago Union Station|Union Station]]). The tracks then emerge from a portal near {{cta|UIC-Halsted}} in the median of the [[Interstate 290 (Illinois)|Eisenhower Expressway]] (Interstate 290) and continue west.

=== Forest Park branch ===
{{Congress branch (CTA)}}
After exiting the subway, the tracks continue west in the median of the Eisenhower Expressway as the '''Forest Park branch''', formerly called the '''Congress branch''', successor to the Garfield Park Branch.

Immediately west of {{cta|Racine|Blue}}, the Forest Park branch tracks diverge to permit a ramp up to the Douglas Branch elevated structure. This ramp was formerly used in revenue service from 1958 to 2008 when the Blue Line operated over the Douglas branch and the Forest Park branch.

With the replacement of Douglas branch Blue Line service with the Pink Line, the ramp is now [[non-revenue track]]age used for the transfer of 5000 series trains that the Blue Line borrows from the Pink Line for weekday rush hour service. The Forest Park branch remains in the median of the expressway through the west side of Chicago until it reaches a portal at Lotus Avenue.

At this point, the tracks pass beneath the eastbound expressway lanes before emerging on the south side of the expressway next to the [[CSX Transportation]] ([[Baltimore and Ohio Chicago Terminal Railroad]]) tracks. The route passes through [[Oak Park, Illinois|Oak Park]] and into [[Forest Park, Illinois|Forest Park]]. In the vicinity of Desplaines Avenue the tracks rise and make an S-curve north over the expressway before terminating at the {{cta|Forest Park}} station.