It is the busiest line on the "L" system, with an average of 108,303 passengers boarding each weekday in 2023[1] The route is 21.8 miles (35.1 km) long with a total of 33 stations.

[3] The northern terminus of the Red Line is Howard in the Rogers Park neighborhood of Chicago, on the north side.

South of Belmont, Red, Brown and Purple Line Express trains run side-by-side on the four track North Side "L" to Armitage.

Red Line trains run on the two middle tracks, only making two stops at Belmont & Fullerton and skipping Wellington, Diversey and Armitage.

The Purple Line shares the distinction only when it runs its weekday rush hour route.

Beyond the interchange, the Dan Ryan Expressway and Bishop Ford Freeway both continue towards the south city limits without a transit line in the median strips, but were built with wide grass medians in which future extensions of the rapid transit line remain an option.

Between approximately midnight and 5:30 a.m., night owl service on the Red Line ranges between ten and fifteen minutes (4–6 tph).

The route was extended to Central Street in Evanston on May 16, 1908, via leased and electrified trackage belonging to the Chicago, Milwaukee and St. Paul Railway.

The ground-level section between Leland Avenue and Howard Street was elevated on a concrete embankment structure and widened to four tracks in 1922.

By providing an express route free of the most restrictive curves on the Chicago "L" and shorter than the old line it supplemented, the subway reduced running time by as much as eleven minutes for a one-way trip.

When the controversial subway project was cancelled in 1979, the Lake-Dan Ryan service remained and lasted for 24 years.

For much of the 20th century, the Howard–Englewood/Jackson Park route was equally compatible in terms of passenger service until the late 1960s through the 1970s.

A further operational benefit of this switch was that this freed up capacity in the Loop needed for the addition of the Orange Line to Midway Airport.

The Dan Ryan Branch of the Red Line underwent a rehabilitation period to improve its aging infrastructure which ended in early 2007.

[11] This work included upgrading the power and signal systems, and rehabilitating the stations with improved lighting, a cleaner appearance, and new escalators and elevators.

[14] The program monitors the full route of the Red Line, excluding the Loyola, Bryn Mawr, Sheridan, or Wilson station.

The stations are listed in order, starting at Granville, then Morse, Thorndale, Argyle, Berwyn, Lawrence and finally Jarvis.

[16] The Red & Purple Modernization Project will include a redesign of a diamond junction north of Belmont Station into a flyover for Brown Line trains.

[17] The project was criticized by 2015 mayoral candidate Chuy García and local residents in the Lakeview neighborhood who organized a referendum to stop it.

The two bus routes would travel south from the 95th/Dan Ryan terminal either down Halsted Street or Michigan Avenue, while the heavy rail routes left for consideration were the Halsted and Michigan corridors (either underground or elevated) as well as the Union Pacific Railroad corridor (elevated or trench), which would traverse southeastward toward the South Shore Line.

[28][29] The alignment consists of a new elevated rail line between 95th/Dan Ryan and a new terminal station at 130th Street, paralleling the Union Pacific Railroad and the South Shore Line, through the Far South Side neighborhoods of Roseland, Washington Heights, West Pullman, and Riverdale.