The 'L' (sometimes written as "L", El, EL, or 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 second largest rapid transit system in total track mileage in the United States, after the New York City Subway, and is the third busiest rail mass transit system in the United States, after the New York City Subway and the Washington Metro. Chicago's 'L' is one of four heavy rail systems in the United States (the 'L', New York City Subway, PATH, and the PATCO Speedline) that provide 24-hour service on at least some portions. The oldest sections of the 'L' started operations in 1892, making it the second-oldest rapid transit system in the Americas, after Boston. 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 mainly focusing transit towards the Loop. Although the 'L' gained its nickname because large parts of the system are elevated, portions of the network are also in subway tunnels, at grade level, or open cut.

On average 788,415 people ride the 'L' each weekday, 519,959 each Saturday, and 377,308 each Sunday. Annual ridership for 2011 was 221.6 million. In a 2005 poll, Chicago Tribune readers voted it one of the "seven wonders of Chicago," behind the lakefront and Wrigley Field but ahead of Willis Tower (formerly the Sears Tower), the Water Tower, the University of Chicago, and the Museum of Science and Industry.

en.wikipedia.org/wiki/Chicago_%27L%27