High Quality Content by WIKIPEDIA articles! The Vienna U-Bahn (an abbreviation of Untergrundbahn, or underground railway) is a rapid transit (metro) system consisting of five lines. It is the backbone of one of the best performing public transport systems worldwide according to UITP (International Association of Public Transport) in June 2009. More than 1.3 million passengers use the Vienna U-Bahn every day. The network is undergoing expansion and rolling stock renewal. Since 1969, 200 million euros have been invested annually into the extension of the Vienna U-Bahn.