The Union Loop, also known as the Chicago L or the Union Elevated Railroad, lies at the center of Chicago's rapid transit system.

It is formed by a series of elevated railroads that connect the three main elevated railway lines, the South Side Elevated Railroad, the Lake Street Elevated Railroad and the Metropolitan West Side Elevated Railroad.

he Loop was born in political scandal: upon completion, all the rail lines running downtown had to pay Yerkes's operation a fee, which raised fares for commuters; when Yerkes, after bribery of the state legislature, secured legislation by which he claimed a fifty-year franchise, the resulting furor drove him out of town and ushered in a short-lived era of "Progressive Reform" in Chicago.[7]

Originally there were 12 stations, with three stations on each side of The Loop. The construction of the west-leg of the Union Loop over Wells Street required the removal of the southern platform of the Fifth/Lake station. The addition of the Northwestern Elevated Railroad caused the removal of the rest of the station as the remaining platform sat across the new road's entry point. This left 11 stations, two on the north leg of the loop and three on each other leg.