On an average weekday, 759,866 passengers ride the "L",[1] making it the second-busiest rapid transit system in the United States, behind the New York City Subway.
[2] The system began as three separate companies, which built lines traveling from Chicago's central business district to the south and the west.
Initially, the "L" lines operated independently of each other, but in 1897, they were combined into one physically unified system with the completion of the Union Loop and connecting trackage.
[4] In 1900, the Northwestern Elevated Railroad entered operation,[5] finalizing the basic structure of the system: a hub and spoke distribution paradigm radiating north, west, and south from downtown Chicago.
[6] Starting in 1948, the CTA began systematically shutting down many stations and lines that saw little use in order to improve service and reduce costs.