The Blue Line is a 26.93-mile-long (43.34 km) Chicago "L" line which runs 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 in Forest Park, with a total of 33 stations (11 on the Forest Park branch, 9 in the Milwaukee–Dearborn subway and 13 on the O'Hare branch). At about 27 miles, it is the longest line on the Chicago "L" system and second busiest, and one of the longest local subway/elevated lines in the world. It has an average of 72,475 passengers boarding each weekday in 2023.
Chicago's Blue Line and Red Line offer 24-hour service, every day, year-round. This makes Chicago, New York City, and Copenhagen the only three cities in the world to offer local nonstop rail service throughout their city limits 24 hours a day, seven days a week. The Blue Line is the only line in Chicago with more than one station having the exact same name. (The Blue Line has two stations at Harlem Avenue: one in the Kennedy Expressway on the Northwest side and one on the Eisenhower Expressway in Forest Park, Illinois. It also has two stations on Western Avenue: one on the segment between downtown and O'Hare, and one immediately west of downtown.) The Blue Line also has two in-system transfers (both in the Loop), and does not share tracks with any other 'L' line.
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