[note 2] The oldest sections of the Chicago "L" started operations in 1892,[8] making it the second-oldest rapid transit system in the Americas, after New York City's elevated lines.

The Metropolitan was the United States' first non-exhibition rapid transit system powered by electric traction motors,[15] a technology whose practicality had been demonstrated in 1890 on the "intramural railway" at the World Fair that had been held in Chicago.

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.

[17] 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.

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.

[17] 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 and 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.

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.

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.

[8] Due to the Loop Flood in April 1992, ridership was at 418,000 that year[24] because CTA was forced to suspend operation for several weeks in both the State and Dearborn subways, used by the most heavily traveled lines.

Ridership on the North Side Brown Line, for instance, has increased 83% since 1979, necessitating a station reconstruction project to accommodate longer trains.

For example, ridership at the linked Roosevelt stops on the Green, Orange, and Red Lines,[note 3] which serve the burgeoning South Loop neighborhood, has tripled since 1992, with an average of 8,000 boardings per weekday.

The 2003 Chicago Central Area Plan proposed construction of a Green Line station at Cermak, between Chinatown and the McCormick Place convention center, in expectation of continued density growth in the vicinity.

[8] Ventra enables passengers to purchase individual tickets, passes, or transit value online, by smart phone, or at participating retail locations.

[42] With the DC propulsion of the previous series, they utilize dynamic braking which converts the excess kinetic energy into heat within a resistor bank.

[44] State-owned manufacturer CRRC Sifang America (China Rail Rolling Stock Corporation) won the contract, besting the other major competitor, Bombardier from Canada by $226 million.

[citation needed] 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.

[68] While various mayors of Chicago had recognized the importance of reliable public transit, Rahm Emanuel received credit for making improving service a top priority.

"We are looking forward to providing our south Red Line customers with improved stations that are cleaner, brighter and better than they have been in years," said CTA President Forrest Claypool.

[60] In late 2015, extensive 4G wireless coverage was added to both Blue and Red Line subways, with the $32.5 million installation cost paid for by T-Mobile, Sprint, AT&T and Verizon.

The century-old station now includes accessible elevators, escalators, new security cameras, three entrances, wider stairwells, additional turnstiles, larger platforms, new lights and signage, as well as bus and train trackers.

In the final days of the Barack Obama administration, the federal government agreed to provide $957 million in funding in total; the rest would come from a tax hike on property owners who lived within 0.5 miles (800 m) of the Red Line.

[91] In December 2022, the City Council approved the creation of a district that will send nearly $1 billion in tax revenue over the next few decades to extend the Red Line south of 95th Street, a major step toward completing the project after a half-century of false starts.

[99] In 2009, CTA released the results of its Alternatives Analysis Screen 3, in which it decided to begin early engineering work on Phase 2, due to its simple alignment through unpopulated areas and its relatively low cost (estimated to be $1.1 billion).

[109] Numerous plans have been advanced over the years to reorganize downtown Chicago rapid transit service, originally with the intention of replacing the elevated Loop lines with subways.

At present the "L" does not provide direct service between the Metra commuter rail terminals in the West Loop and Michigan Avenue, the principal shopping district, nor does it offer convenient access to popular downtown destinations such as Navy Pier, Soldier Field, and McCormick Place.

It would then continue south on Clinton until 16th Street, where it would turn east, cross the river again, and rejoin the Red Line just north of the current Cermak-Chinatown stop.

[117] In comments posted to her blog in 2006, CTA chair Carole Brown said, "I would support premium rail service only if it brought significant new operating dollars, capital funding, or other efficiencies to CTA… The most compelling reason to proceed with the project is the opportunity to connect the Blue and Red subway tunnels," which are one block apart downtown.

[139] On September 2, 2024, four people were killed in a mass shooting aboard a Blue Line train as it traveled between the Oak Park and Harlem stations.