The Blue Line (O'Hare-Congress & O'Hare-Douglas Services), consists of a 19.5 mile 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-Congress subway, and across the West Side with two branches at its southwest end, one to Forest Park (Congress) and the other to Cicero (Douglas). It is the CTA's second busiest rail line, with more than 119,700 station entrances and 147,000 passengers boarding each weekday. The route's full length is 34.6 miles with a total of 44 stations.
The Blue Line and Red Line are the only two routes on the CTA rail system to presently run 24 hours a day. Service to 54th/Cermak only operates weekday rush hours. It operates from 5:30 a.m. until 9:30 a.m. and again from 2:30 p.m. until 6:30 p.m.
The Blue Line was formerly called the West-Northwest route 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, however many Chicago historians and expert 'L' riders still refer to the old route names.
