<Tr> <Td> <P> </P> </Td> </Tr> <P> The Chicago "L" (short for "elevated") is the rapid transit system serving the city of Chicago and some of its surrounding suburbs in the U.S. state of Illinois . It is operated by the Chicago Transit Authority (CTA). 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) long, and the second - busiest rail mass transit system in the United States, after the New York City Subway . </P> <P> Chicago's "L" provides 24 - hour service on some portions of its network, being one of only five rapid transit systems in the United States to do so . 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 . </P> <P> The "L" has been credited with fostering the growth of Chicago's dense city core that is one of the city's distinguishing features . The "L" consists of eight rapid transit lines laid out in a spoke--hub distribution paradigm focusing transit towards the Loop . Although the "L" gained its name because large parts of the system are elevated, portions of the network are also in subway tunnels, at grade level, or open cut . </P>

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