Copenhagen Metro in the context of "Indre By"

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. 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 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 2024, the system had 127,463,400 rides, or about 454,300 per weekday in the third quarter of 2025.

The "L" provides 24-hour service on the Red and Blue Lines, making Chicago, New York City, and Copenhagen the only three cities in the world to offer 24-hour train service on some of their lines throughout their respective city limits. 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 large parts of the system run on elevated track. Portions of the network are in subway tunnels, at grade level, or in open cuts.