Congress Branch

Blue Line

Company type	Rapid transit route
Industry	Public transportation
Predecessor	Metropolitan West Side Elevated Railroad
Founded	1895
Headquarters	Chicago , United States
Area served	Chicago, Rosemont, Oak Park, Forest Park
Products	Rapid transit service
Parent	Chicago Transit Authority

The Blue Line is a Chicago "L" route extending from O'Hare International Airport through the downtown area via the Milwaukee–Dearborn subway, terminating southwest in Forest Park. It comprises 33 stations in total: 11 along the Forest Park branch, 9 within the subway segment, and 13 on the O'Hare branch. This line holds the distinction of being the system's longest and ranks second in ridership, averaging 72,475 passengers on weekdays in 2023.

Together with the Red Line, the Blue Line provides continuous 24/7 service throughout the year, positioning Chicago among only three cities globally to offer nonstop local rail transit within city boundaries. Notably, this line features two pairs of stations sharing identical names located on Harlem Avenue and Western Avenue, and it includes two internal transfer points within the Loop. The Blue Line operates entirely on its own tracks without sharing with other routes.

Before adopting its color-coded identity, it was referred to as the West-Northwest Route or the O'Hare-Congress-Douglas route. In 1993, its branches were renamed after their terminal points—Forest Park and 54th/Cermak. Service along the Douglas branch was discontinued and replaced by the Pink Line as of April 2008.

The Blue Line is among five Chicago "L" routes that extend beyond city limits into suburban areas, serving communities such as Rosemont, Oak Park, and Forest Park.

O'Hare branch

The O'Hare branch represents the Blue Line’s longest stretch (), incorporating both its earliest and most recent track segments. It starts at O'Hare International Airport in a subterranean station located beneath the main parking structure, offering direct pedestrian connections to Terminals 1, 2, and 3. The track then surfaces in the median of Interstate 190, just northwest of Terminal 5, approximately one mile west of Mannheim Road.

Proceeding eastward through Rosemont, there is a station at River Road which houses the northern rail yard and functioned as a temporary terminal between 1983 and 1984 during construction of the O’Hare station. The line subsequently tunnels beneath the interchange of the Kennedy Expressway and Northwest Tollway near the Des Plaines River.

Continuing along the median of Interstate 90—the Kennedy Expressway—it serves stops at , , , , , and . Between Montrose and Irving Park stations, it passes through a tunnel under an express lane exit. After passing Addison station heading south, the route enters a subway segment that turns southward beneath Kimball Avenue and Milwaukee Avenue, traversing through Logan Square with stops at and .

South of Logan Square, the line rises above ground onto an elevated structure running parallel to Milwaukee Avenue. This section dates back to 1895, making it both the oldest portion of the Blue Line and its sole elevated viaduct. The three stations here—, , and —feature side platforms instead of island platforms.

Milwaukee–Dearborn subway

At the intersection of Ashland and Milwaukee Avenues, the Blue Line descends underground once again, following Milwaukee Avenue southeast toward downtown with stops at , , and . The line then veers eastward beneath Lake Street, crossing under the Chicago River, stopping at , where transfers to Loop 'L' services are available.

Beyond Clark/Lake station, tracks curve southward beneath Dearborn Street with one continuous platform serving , , and .

After Jackson station, the route turns west beneath Ida B. Wells Drive, making stops at and , which is near Chicago Union Station. Shortly thereafter, tracks emerge close to , entering the median of the Eisenhower Expressway (Interstate 290) as they continue westward.

Forest Park branch

Upon leaving the subway, the tracks proceed westward within the Eisenhower Expressway median, forming the Forest Park branch, which was previously known as the Congress branch and is still internally identified by that name. This line serves as the successor to the former Garfield Park Branch.

West of , the Forest Park branch tracks split off toward a ramp connecting to the Douglas Branch elevated structure. This ramp was actively used for revenue service from 1958 until 2008, during which time the Blue Line operated on both branches. Since the Pink Line took over Douglas branch service, this ramp has been relegated to non-revenue track status and is primarily utilized for transferring 5000 series trains loaned to the Blue Line during weekday peak periods. The branch continues along the expressway median through Chicago’s western neighborhoods until reaching a portal near Lotus Avenue.

At this point, the tracks pass beneath the eastbound lanes and then run adjacent to CSX Transportation (Baltimore and Ohio Chicago Terminal Railroad) lines, continuing through Oak Park and into Forest Park. Close to Desplaines Avenue, the tracks elevate and curve northward over the expressway before ending at station.

Ridership on the Forest Park branch has declined due to competition from the Green and Pink Lines, as well as its location within a highway median, which limits opportunities for dense residential development and results in stations exposed to air and noise pollution. Moreover, deferred maintenance beyond Illinois Medical District station has led to accelerated track degradation. The proportion of slow zones increased significantly from 13.1% in 2016 to 61.6% in 2020, then further to 72.4% in 2024, and is projected to reach 79.2% by 2025.

Phase 1 of the Forest Park Branch Rebuild, which included improvements to tracks and stations between LaSalle and Illinois Medical District station, was finalized in 2023. However, plans for subsequent phases aimed at refurbishing the remaining sections of the branch have yet to be announced.

Operating hours and headways

Similar to the Red Line, the Blue Line provides continuous service throughout each day. The majority of trains operate between O'Hare and Forest Park stations, though some terminate at intermediate points. During weekday rush hours, trains run frequently with intervals of 10–20 tph (trains per hour), including short-turn services between UIC-Halsted and Jefferson Park or Rosemont. Midday and overnight schedules offer service at rates of 6–8 tph.

On Saturdays, service begins with 8 tph in the early morning, increases to 10 tph during daytime hours, then decreases back to 8 tph overnight. Sunday service features early morning frequencies of 6–8 tph, steady 10 tph throughout most of the day, and reduces to 6 tph at night. During weekend daytime hours, every other train operates only between O'Hare and UIC-Halsted, effectively doubling headways to 5 tph. Overnight service between midnight and 5:30 a.m. runs at frequencies of 3–4 tph.

Rolling stock

The Blue Line's fleet includes 2600-series, 3200-series, and 7000-series railcars. In 2018, several 2600-series cars were replaced by refurbished 3200-series units transferred from the Brown and Orange Lines, with some displaced 2600-series cars reassigned to Orange Line service. Additionally, two 5000-series trainsets assigned primarily to the Pink Line operate on the Blue Line during weekday rush hours but remain officially designated as Pink Line equipment.

History

The origins of the Blue Line trace back to the Metropolitan West Side Elevated Railroad, which commenced service on Chicago's West Side in 1895. Its first segment opened on May 6, 1895, running near Van Buren Street from Canal and Jackson Streets to Marshfield Avenue, then continuing north along Paulina Street to Damen and Milwaukee Avenues. By May 25, 1895, the line had extended to reach Logan Square.

On June 19, 1895, the Garfield Park Branch began operating westward from Marshfield Avenue to Cicero Avenue. Later in 1905, service expanded over the Aurora, Elgin and Chicago Railroad tracks to a terminal at Desplaines Avenue, eventually reaching Westchester in 1926 before being discontinued in 1951 due to declining ridership.

Other branches included the Humboldt Park Branch, which ran west along North Avenue from Damen to Lawndale starting July 29, 1895, and the Douglas Park Branch that launched on April 28, 1896. The Douglas branch gradually extended through Berwyn by 1924 but was later shortened back to Cicero.

Loop service began for the Metropolitan West Side Elevated on October 11, 1897, with a rush-hour stub terminal added in 1904. Control of the system transferred to the Chicago Transit Authority in 1947, which then implemented significant service cuts over subsequent decades.

A major modernization effort commenced on February 25, 1951, when the CTA opened the Milwaukee-Dearborn Subway. This new subway connected the Logan Square Branch directly to the Loop, enabling faster access downtown. As a result, parts of the original elevated structure were decommissioned; today, only the Paulina Connector remains operational. The Humboldt Park Branch was reduced to shuttle service before its closure in 1952.

The Garfield Park elevated line was replaced by the Congress line on June 22, 1958. This innovative design combined rapid transit rail with an expressway median and linked the Milwaukee-Dearborn Subway with Forest Park via the Chicago River corridor. The Loomis Ramp allowed Douglas trains access to this subway system, integrating multiple routes into what became known as the Congress/Douglas-Milwaukee Line.

A federally funded five-mile extension opened on February 1, 1970, connecting Logan Square to Jefferson Park through a subway link and Kennedy Expressway median. Trains diverged from old elevated tracks near Logan Square into tunnels before surfacing along the expressway toward Jefferson Park terminal. Growing ridership prompted further expansion toward O'Hare Airport beginning in March 1980; segments opened incrementally between February 1983 and September 1984.

On February 21, 1993, CTA adopted color-coded route names; at this time, the West-Northwest route was designated as the Blue Line.

By October 15, 2015, CTA had completed installing 4G wireless coverage between Logan Square and Belmont, positioning itself as a leader in providing wireless connectivity within subway tunnels and stations by year-end.

Douglas branch

The Douglas branch operated as part of the Blue Line until April 28, 2008, when CTA replaced Blue Line service with the Pink Line. The Loomis ramp connecting the Congress branch with Douglas remains intact for non-revenue equipment movements and serves as the only track connection between the Blue Line and other parts of the system.

On April 26, 1998, budgetary constraints led to discontinuing overnight and weekend service on the Douglas Branch; operations were limited to weekdays from 4 a.m. until 1 a.m., effectively doubling Congress (Forest Park) line frequency during most daytime hours.

While CTA attributed these reductions to low ridership levels, community advocates highlighted deteriorating infrastructure and funding deficiencies as underlying causes and argued that this reflected a lack of commitment to West Side transit service. On September 10, 2001, CTA initiated an extensive rehabilitation of the Douglas Branch that concluded on January 8, 2005. This overhaul included new elevated structures and tracks, station reconstructions, updated communication systems, and power system enhancements. Weekend service was reinstated starting January 1, 2005.

In early 2005, CTA proposed rerouting Douglas Branch trains via the refurbished Paulina Connector to join the Lake Street Green Line, allowing Douglas trains access to the Loop elevated for the first time since 1958. This plan led to creation of what is now known as the Pink Line, enabling an increase in Blue Line trains heading to Forest Park by separating services between Forest Park and the 54th/Cermak terminals. However, due to community concerns about Pink Line capacity constraints during rush hours, limited Douglas Branch Blue Line service was maintained during peak periods.

On February 15, 2006, CTA approved distinct operations for the Douglas Branch: non-rush hour trains would run via the Loop using Green Line tracks and Paulina Connector; rush hour trains served both this route and continued via Milwaukee-Dearborn Subway. These changes commenced with a six-month trial beginning June 25, 2006. After evaluation in early 2007 confirmed positive results, CTA retained Pink Line service permanently.

Starting April 28, 2008, CTA conducted a six-month trial that discontinued all Blue Line operations on Douglas Branch. Although termed an experiment initially, signage changes suggested permanent removal. All Douglas Branch trains were shifted exclusively to Pink Line operation. On December 4, 2008, CTA formally ended Blue Line service on Douglas and established Pink Line as permanent.

Accidents and incidents

• On July 11, 2006, a derailment in the Milwaukee-Dearborn Subway on the Blue Line triggered a fire accompanied by heavy smoke, resulting in several cases of smoke inhalation but no deaths. This event caused a temporary suspension of subway operations in Chicago amid increased security measures following train bombings in Mumbai earlier that same day.
• On September 30, 2013, a collision occurred between two Blue Line trains at Harlem station on the Congress branch, injuring 33 individuals. The accident happened when an out-of-service train, left powered on in Desplaines Yard and moving against the outbound train’s direction, struck it. The National Transportation Safety Board (NTSB) determined the cause was water intrusion in control cables combined with inadequate securing of unattended equipment. Limited service resumed after the investigation concluded.
• During the early morning hours of March 24, 2014, a Blue Line train derailed at O'Hare station, resulting in injuries to 32 passengers; none were life-threatening. Full station service was restored by March 30.
• On April 10, 2019, another derailment near O'Hare station injured one person. The CTA attributed this incident to human error by its personnel.
• A mass shooting took place on September 2, 2024, aboard a Blue Line train traveling between Oak Park and Harlem stations, causing four fatalities. The suspect was captured after boarding the Pink Line.

Line extensions

Initial plans to extend the Blue Line westward beyond O'Hare toward Schaumburg were reevaluated due to new transit projects such as the Metra STAR Line. In 2008, the Regional Transit Authority proposed extending the line 13.3 miles from Forest Park to Yorktown Center in Lombard, supplemented by feeder bus routes; this proposal was incorporated into the Chicago region’s 2030 transportation master plan.

A proposed infill station at Nagle and Bryn Mawr Avenues—situated between Jefferson Park and Harlem stations and representing one of the system’s longest station gaps—was deferred in 2013 but remains under consideration for future development.

In December 2016, Pace introduced the I-90 Express Bus Rapid Transit (BRT) service, effectively replacing previous Blue Line extension and STAR Line proposals by offering expedited transit along I-90 to Elgin.

Additional tracks

The right-of-way along the Congress Branch was designed with space for extra tracks: a single additional track between Forest Park and Kenton Avenue and two more tracks from Kenton to the UIC-Halsted tunnels. These provisions were originally intended for use by the Chicago Aurora and Elgin Railroad (CA&E), which ended passenger operations in 1957 before these tracks were constructed.

Although CTA explored options such as implementing express tracks or rerouting the Green Line onto the Paulina Elevated structure (now part of the Pink Line), they ultimately opted to establish the Pink Line as a separate service instead.

Stub tunnels

At UIC-Halsted, the Congress Branch features four portals rather than two: two additional portals lie north of those used by the Blue Line and extend only a short distance beyond them. These were constructed with future expansion in mind, including plans for a new CA&E terminal line. Earlier proposals envisioned a loop subway system connecting Congress, Dearborn, Lake, and Clinton streets following completion of the Milwaukee-Dearborn-Congress Subway between 1951 and 1958, as well as a shuttle subway beneath Jackson Street linking to Grant Park.

Between 1968 and 1978, plans surfaced for a downtown subway corridor starting at UIC-Halsted via these northern portals, running north beneath Des Plaines Street to Monroe Street before turning east toward Grant Park and Millennium Park. This corridor would have branched to serve North Michigan Avenue and McCormick Place via the Metra Electric right-of-way. Although never realized, this route remains part of ongoing planning since both Crosstown and Loop Subway projects were postponed in 1979.

Within the Milwaukee-Dearborn Subway between Grand/Milwaukee and Clark/Lake stations, two stub tunnels extend westward beneath Lake Street while active tracks veer northwest under Milwaukee Avenue. This stacked junction—a construction from the 1940s—was intended for an unbuilt connection or for replacing part of the Lake Street Elevated line with subway service. During the late 1960s through the 1970s, it was also proposed as a link between the Dearborn Subway and a high-speed subway along Randolph Street designed to replace segments of the Lake Street 'L' east of Damen Avenue.

Station directory

Municipality	Neighborhood	Station	Transfers
Chicago	O'Hare	Template:Cta	Template:Rint O'Hare International Airport Template:Rint Airport Transit System
Rosemont		Template:Cta Template:Rint	Template:Rint Pace buses: 221, 223, 230, 303, 330, 332, 600, 605, 606, 611
Chicago	O'Hare	Template:Cta Template:Rint	Template:Rint CTA Bus: 81W Template:Rint Pace buses: 209, 240, 241, 290, 331 Template:Rint Greyhound Lines
	Norwood Park	Template:Cta Template:Rint	Template:Rint CTA Buses: 88, 90 Template:Rint Pace bus: 423
	Jefferson Park	Template:Cta	Template:Rint Metra trains: Template:Rcb Template:Rint CTA Buses: 56, 68, 81, 81W, 85, 85A, 88, 91, 92 Template:Rint Pace buses: 225, 226, 270 Template:Rint Pace BRT: Pace Pulse