Runs from O'Hare International Airport to Desplaines Avenue, Forest Park in the west suburbs via the Northwest Side, downtown in the Dearborn Subway, and the West Side.

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O'Hare | Milwaukee-Dearborn Subway | Forest Park

Service Notes:

The Blue Line was created in 1958, then called the West-Northwest Route, when the Milwaukee line was through-routed via the Milwaukee-Dearborn Subway with the then-new Congress line and existing Douglas branch.

On a practical level, the Blue Line is the modern ancestor of the lines of the Metropolitan West Side Elevated Railroad, a private "L" company that began service in 1895 serving the West and Northwest sides. Although the actual service pattern of the "Met" was quite different -- rather than a through-routed "horseshoe"-shaped route, the Met was a service that began in the Loop, extended west two miles on a main line, then branched into four lines and fanned out to the west, southwest, and northwest -- the basic alignments are the same.

The Douglas branch was formerly the longest section that remained from the old Metropolitan system, although following the 2001-05 renovation of the branch only the 1.5 north-south segment of the branch along Paulina Avenue still consists of the 1890s steel structure (the rest of the structure and all of the stations have been result), and as of 2008 is no longer part of the Blue Line route. The 2.2-mile elevated portion of the O'Hare branch between south of Logan Square and south of Damen is perhaps the best preserved example of the old Met Elevated, with most of its elevated structure and two of the three stations on this stretch still original, although this represents only a small portion of the Met's Northwest branch. The Met's Garfield Park branch and main line were replaced wholesale with the adjacent and parallel Congress Line in the 1950s. The same decade, the Met's Humboldt Park branch closed and little remains of it.

The Milwaukee-Dearborn Subway, which allowed the West Side "L" to be through-routed rather than operate as a trunk-and-branch operation, was started by the WPA as a New Deal public works project. Work on the subway was suspended during World War II due to materials and manpower shortages, but was resumed after the war and opened in 1951.

As part of the city's comprehensive plan for 'subways and superhighways', planned and carried out in the 1930s to 1950s by a city department of that name, the Congress Line was designed as a modern, high-speed replacement for the parallel Garfield Park line. Placed in the median of the Congress Superhighway (today called the Eisenhower Expressway, I-290), the Congress Line was the nation's first rapid transit line in a highway median, a model that was subsequently adopted by cities all over the United States.

The West-Northwest Route was extended twice after being created, both following the model begun by the Congress Line. The Milwaukee Line was extended first to Jefferson Park in the far Northwest Side of the city in 1970 via the median of the Kennedy Expressway (I-90/94), then again to O'Hare Airport in 1984 via the same median.

In 1993, the West-Northwest Route was renamed the Blue Line, following the CTA's new color-coded nomenclature for its "L" lines. At the same time, the Congress branch was renamed the "Forest Park branch" and the Douglas branch was renamed the "Cermak branch", with new destination-specific railcar destination signs to match, although many longtime riders still use the original names.

From September 2001 to January 2005, the CTA undertook a $482.6 million renovation of the Cermak (Douglas) branch of the Blue Line. The project rehabilitated 5.5 miles of elevated structure, eliminating slow zones and speeding up travel times for customers getting them from the terminal at 54th/Cermak to the Loop in 25 minutes or less instead of the 45 minutes it took prior to reconstruction. The project also rebuilt eight stations (the other three having already been rebuilt recently), making all stations on the branch ADA-accessible; replaced five miles of track, rail ties and foot walks, and the support structure; and installed a new signal communications system. Kiewit/Delgado, AJV (A Joint Venture), of Elgin, IL, was the construction contractor for the project.

On June 25, 2006, most trains from 54th/Cermak were rerouted to the Loop via the Paulina Connector and Lake branch as the new Pink Line. Blue Line trains continued to run between 54/Cermak and O'Hare as well, but only during weekday rush hours. This continued until Friday, April 25, 2008, when the last Blue Line trains operated to 54th/Cermak. Afterward, all service to 54th/Cermak was provided by the Pink Line. Although ridership had risen overall since the introduction of the Pink Line, Blue Line Cermak service was eliminated because its trains had consistently low ridership on a person-per-railcar-basis.

The Blue Line serves several points of interest, including O'Hare International Airport, City Hall/County Building, Daley Center, Thompson Center, Federal Center, the Board of Trade, the University of Illinois at Chicago, and the Medical District.