World's Most Crowded Subways
No. 20 Vienna
Annual Ridership: 534 million
Vienna’s U-Bahn makes stops at prominent sights like the museum quarter and Rathaus. The system was originally built as a tram network in the late 1800s and was later converted into a metro system. (Plans for the subway’s construction were interrupted by World War I and discontinued after the country’s poor postwar economic state.) In its current form, the metro wasn’t operational until the 1970s, but elegant old-world stations like Karlsplatz Stadtbahn recall the transit system’s early days.
Source: World Metro Database, 2011