The Chicago "L" (short for "elevated") is a rapid transit system serving the city of Chicago and some of its surrounding suburbs in the U.S. state of Illinois. The system is operated by the Chicago Transit Authority (CTA), one of the three service boards of the Northern Illinois Transit Authority (NITA). It is the fourth-largest rapid transit system in the United States in terms of total route length, at 102.8 miles (165.4 km), as of 2014, and the third-busiest rapid transit system in the United States after the New York City Subway and the Washington Metro. As of January 2024, the "L" had 1,480 rail cars operating across eight different routes on 224.1 miles of track. CTA trains make about 1,888 trips each day servicing 146 train stations. In 2025, the system had 135,202,800 rides, or about 447,000 per weekday in the second quarter of 2026.
The "L" provides 24-hour service on the Red and Blue Lines, making Chicago, New York City, London and Copenhagen the only four cities in the world to offer 24-hour train service on some of their lines throughout their respective city limits. The Orange Line has planned 24-hour service beginning in 2026. The oldest sections of the Chicago "L" started operations in 1892, making it the second-oldest rapid transit system in the Americas, after New York City's elevated lines. The "L" gained its name from "el" because most parts of the system run on elevated track, although portions of the network are in subway tunnels, at grade level, or in open cuts.
The "L" has been credited for fostering the growth of Chicago's dense city core that is one of the city's distinguishing features. And according to urban engineer Christof Speiler, the system stands out in the United States because it continued to invest in services even through the post-World-War era growth of the expressway; its general use of alleyways instead of streets throughout its history, and expressway medians after the war, better knit the system into the city, and in pioneering ways. It consists of eight rapid transit lines laid out in a spoke–hub distribution paradigm focusing transit toward the Loop.
In a 2005 poll, Chicago Tribune readers voted it one of the "seven wonders of Chicago", behind the lakefront and Wrigley Field, and ahead of Willis Tower (formerly the Sears Tower), the Water Tower, the University of Chicago, and the Museum of Science and Industry.
History
Pre-CTA era
The first "L", the Chicago and South Side Rapid Transit Railroad, began revenue service on June 6, 1892, when a steam locomotive pulling four wooden coaches, carrying more than a couple of dozen people, departed the 39th Street station and arrived at the Congress Street Terminal 14 minutes later, over tracks that are still in use by the Green Line. Over the next year, service was extended to 63rd Street and Stony Island Avenue, then the Transportation Building of the World's Columbian Exposition in Jackson Park.
In 1893, trains began running on the Lake Street Elevated Railroad and in 1895 on the Metropolitan West Side Elevated, which had lines to Douglas Park, Garfield Park (since replaced), Humboldt Park (since demolished), and Logan Square. The Metropolitan was the United States' first non-exhibition rapid transit system powered by electric traction motors, a technology whose practicality had been demonstrated in 1893 on the Columbian Intramural Railway at the World's Columbian Exposition in Chicago. Two years later the South Side "L" introduced multiple-unit control, in which the operator can control all the motorized cars in a train, not just the lead unit. Electrification and MU control remain standard features of most of the world's rapid transit systems.
A drawback of early "L" service was that none of the lines entered the central business district. Instead trains dropped passengers at stub terminals on the periphery due to a state law at the time requiring approval by neighboring property owners for tracks built over public streets, something not easily obtained downtown. This obstacle was overcome by the legendary traction magnate Charles Tyson Yerkes, who went on to play a pivotal role in the development of the London Underground, and who was immortalized by Theodore Dreiser as the ruthless schemer Frank Cowperwood in The Titan (1914) and other novels.
Yerkes, who controlled much of the city's streetcar system, obtained the necessary signatures through cash and guile—at one point he secured a franchise to build a mile-long "L" over Van Buren Street from Wabash Avenue to Halsted Street, extracting the requisite majority from the pliable owners on the western half of the route, then building tracks chiefly over the eastern half, where property owners had opposed him. Designed by noted bridge builder John Alexander Low Waddell, the elevated tracks used a multiple close-rivet system to withstand the forces of the passing trains' kinetic energy.
The Union Loop opened in 1897 and greatly increased the rapid transit system's convenience. Operation on the Yerkes-owned Northwestern Elevated, which built the North Side "L" lines, began three years later, essentially completing the elevated infrastructure in the urban core although extensions and branches continued to be constructed in outlying areas through the 1920s.
After 1911, the "L" lines came under the control of Samuel Insull, president of the Chicago Edison electric utility (now Commonwealth Edison), whose interest stemmed initially from the fact that the trains were the city's largest consumer of electricity. Insull instituted many improvements, including free transfers and through routing, although he did not formally combine the original firms into the Chicago Rapid Transit Company until 1924. He also bought three other Chicago electrified railroads, the Chicago North Shore and Milwaukee Railroad, Chicago Aurora and Elgin Railroad, and South Shore Line interurban lines, and ran the trains of the first two into downtown Chicago via the "L" tracks.
This period of relative prosperity ended when Insull's empire collapsed in 1932, but later in the decade the city, with the help of the federal government, accumulated sufficient funds to begin construction of two subway lines to supplement and, some hoped, permit eventual replacement of the Loop elevated; as early as the 1920s some city leaders wanted to replace the "ugly" elevated tracks. These plans advanced in the 1970s under mayors Richard J. Daley and Michael Bilandic until a public outcry against tearing down the popular "L" began, led by Chicago Tribune columnist Paul Gapp and architect Harry Weese. Instead, then new Mayor Jane Byrne protected the elevated lines and directed their rehabilitation.
The State Street subway opened on October 17, 1943. The Dearborn Subway, on which work had been suspended during World War II, opened on February 25, 1951. The subways were constructed with a secondary purpose of serving as bomb shelters, as evidenced by the close spacing of the support columns (a more extensive plan proposed replacing the entire elevated system with subways). The subways bypassed a number of tight curves and circuitous routings on the original elevated lines (Milwaukee trains, for example, originated on Chicago's northwest side but entered the Loop at the southwest corner), speeding service for many riders.
CTA assumes control
By the 1940s, the financial condition of the "L", and of Chicago mass transit in general, had become too precarious to permit continued operation without subsidies, and the necessary steps were taken to enable a public takeover. In 1947, the Chicago Transit Authority (CTA) acquired the assets of the Chicago Rapid Transit Company and the Chicago Surface Lines, operator of the city's streetcars. Over the next few years CTA modernized the "L", replacing wooden cars with new steel ones and closing lightly used branch lines and stations, many of which had been spaced only a quarter-mile apart.
Rail service to O'Hare International Airport first opened in 1984 and to Midway International Airport in 1993. That same year, the CTA renamed all of its rail lines; they are now identified by color. The CTA introduced fare cards for the first time in 1997.
Skip-stop service
Later, after assuming control of the "L", the CTA introduced A/B skip-stop service. Under this service, trains were designated as either "A" or "B" trains, and stations were alternately designated as "A" stations or "B" stations, with heavily used stations designated as both – "AB". "A" trains would stop only at "A" and "AB" stations, and "B" trains would stop only at "B" and "AB" stations. The system was designed to speed up lines by having trains skip stations while still allowing for frequent service at the heavily used "AB" stations.
A/B skip-stop service debuted on the Lake Street Elevated in 1948, and the service proved effective as travel times were cut by a third. By the 1950s, the service was used throughout the system. All lines used the A/B skip-stop service between the 1950s and the 1990s with the exception of the Evanston and Skokie lines, which were suburban-only lines and did not justify skip-stop service.
On the lines with branches, skip-stop service sent all "A" trains to one branch and "B" trains to another branch. Individual stops were not skipped beyond the points where those branches diverged. As time went by, the time periods which employed skip-stop service gradually decreased, as the waits at "A" and "B" stations became increasingly longer during non-peak service.
By the 1990s, use of the A/B skip-stop system was only used during rush hour service. Another problem was that trains skipping stations to save time still could not pass the train that was directly ahead, so skipping stations was not advantageous in all regards. In 1993, the CTA began to eliminate skip-stop service when it switched the southern branches of the West-South and North-South Lines to improve rider efficiency, creating the current Red and Green Lines. From this point, Green Line trains made all stops along the entire route, while Red Line trains stopped at all stations south of Harrison. The elimination of A/B skip-stop service continued with the opening of the all-stop Orange Line and the conversion of the Brown Line to all-stop service.
In April 1995, the last of the A/B skip-stop system was eliminated with the conversion of the O'Hare branch of the Blue Line and the Howard branch of the Red Line to all-stop service. The removal of skip-stop service resulted in some increases in travel times, and greatly increased ridership at former "A" and "B" stations due to increased train frequencies. Station signage highlighting the former skip-stop patterns would remain into the 2000s, when it was gradually replaced across the system.
New rolling stock
The first air-conditioned cars were introduced in 1964. The last pre–World War II cars were retired in 1973. New lines were built in expressway medians, a technique implemented in Chicago and followed by other cities worldwide. The Congress branch, built in the median of the Eisenhower Expressway, replaced the Garfield Park "L" in 1958. The Dan Ryan branch, built in the median of the Dan Ryan Expressway, opened on September 28, 1969, followed by an extension of the Milwaukee elevated into the Kennedy Expressway in 1970.
System renovation and service improvements
2000–2010
During the 2000s and 2010s, the CTA has completed several renovation and new construction projects.
Pink Line service began on June 25, 2006, though it did not include any new tracks or stations. The Pink Line travels over what was formerly a branch of the Blue Line from the 54th/Cermak terminal in Cicero to the Polk station in Chicago. Pink Line trains then proceed via the Paulina Connector to the Lake Street branch of the Green Line and then clockwise around the Loop elevated via Lake-Wabash-Van Buren-Wells. Douglas trains used the same route between April 4, 1954, and June 22, 1958, after the old Garfield Park "L" line was demolished to make way for the Eisenhower Expressway. The new route, which serves 22 stations, offered more frequent service for riders on both the Congress and Douglas branches. Pink Line trains could be scheduled independently of Blue Line trains, and ran more frequently than the Douglas branch of the Blue Line did.
In late 2007, trains were forced to operate at reduced speed over more than 22% of the system due to deteriorated track, structure, and other problems. By October 2008, system-wide slow zones had been reduced to 9.1% and by January 2010, total slow zones were reduced to 6.3%. CTA's Slow Zone Elimination Project is an ongoing effort to restore track work to conditions where trains no longer have to reduce speeds through deteriorating areas. The Loop received track work in 2012–2013. The Purple Line in Evanston received track work and viaduct replacement in 2011–2013. The Green Line Ashland branch received track work in 2013, prior to the Red Line Dan Ryan branch reconstruction.
The Brown Line Capacity Expansion Project enabled CTA to run eight-car trains on the Brown Line, and rebuilt stations to modern standards, including accessibility. Before the project, Brown Line platforms could only accommodate six-car trains, and increasing ridership led to uncomfortably crowded trains. After several years of construction, eight-car trains began to run at rush hour on the Brown Line in April 2008. The project was completed in December 2009, on time and on budget, with only minor punch list work remaining. The project's total cost was expected to be around $530 million.
2010–present
While various mayors of Chicago had recognized the importance of reliable public transit, Rahm Emanuel received credit for making improving service a top priority. In addition to local funding, he managed to secure federal dollars by lobbying.