CTA Blue Line

CTA Blue Line

The Blue Line consists of a 19.5-mile (31.4 km) (68-minute ride) long trunk line in the Chicago Transit Authority's rapid transit system which extends through Chicago's Loop from O'Hare International Airport at the far northwest end of the city, through downtown via the Milwaukee-Dearborn subway, and across the West Side to its southwest end at Forest Park (Congress). It is the CTA's second busiest rail line, with an average of 186,796 passengers boarding each weekday. The route's full length is 34.6 miles (55.7 km) with a total of 33 stations.

The Blue Line and Red Line are the only two routes on the CTA rail system to currently run 24 hours a day, and is one of only four mass-transit rail lines in the United States to do so (the others being the PATCO Speedline, the PATH lines, and the New York City Subway). Service between O'Hare and 54th/Cermak no longer operates. The Pink Line now serves all stations on the 54th/Cermak branch. The Blue Line is also one of only two lines with more than one station with the same name, with the Green Line being the other. It has two Harlem stations: one in the Kennedy Expressway on the Northwest side, and one on the south side of the Eisenhower Expressway on the West Side. It also has two Western stations: one on the Milwaukee Elevated and one on the Congress Expressway. The Blue Line also has only two in-system 'L' train transfers - both in the downtown area - and also does not share tracks with any other 'L' train services.

Before the adoption of color-coded names, the Blue Line was referred to as the West-Northwest Route (which it is still sometimes referred to as today) or more commonly, the O'Hare-Congress-Douglas route for its three branches. The Congress and Douglas branches were renamed for their respective terminals, Forest Park and 54th/Cermak, when the current color naming system was adopted in 1993. As of May 2008, Blue Line service to 54th/Cermak no longer operates; it has been replaced with the new Pink Line.