The Loop (historically Union Loop) is the 1.79-mile (2.88 km) long circuit of elevated rail that forms the hub of the Chicago „L“ system in the United States. As of 2012, the branch has served 74,651 passengers every weekday. The Loop is so named because the elevated tracks loop around a rectangle formed by Lake Street (north side), Wabash Avenue (east), Van Buren Street (south), and Wells Street (west). The railway loop has given its name to Chicago’s downtown, which is also known as the Loop.
Transit began to appear in Chicago in the latter half of the 19th century as the city grew rapidly, and rapid transit started to be built in the late 1880s. When the first rapid transit lines opened in the 1890s, they were independently owned and each had terminals that were located immediately outside of Chicago’s downtown, where it was considered too expensive and politically inexpedient to build rapid transit. Charles Tyson Yerkes aggregated the competing rapid transit lines and built a loop connecting them, which was constructed and opened in piecemeal fashion between 1895 and 1897, finally completing its last connection in 1900. Upon its completion ridership on the Loop was incredibly high, such that the lines that had closed their terminals outside of downtown had to reopen them to accommodate the surplus rush-hour traffic.
In the latter half of the 20th century, ridership declined and the Loop was threatened with demolition in the 1970s. However, interest in historic preservation occurred in the 1980s, and ridership has stabilized since.