The Vienna U-Bahn, where U-Bahn is an abbreviation of the German term Untergrundbahn, is one of the two rapid transit (metro) systems for Vienna, Austria. The second system is the Vienna S-Bahn. With the October 2013 opening of the 4.2 kilometers (2.6 mi), three-station extension of the U2 line, the five-line U-Bahn network consists of 78.5 kilometers (48.8 mi) of route, serving 98 stations. It is the backbone of one of the best performing public transport systems worldwide according to UITP in June 2009. More than 1.3 million passengers rode the Vienna U-Bahn every day in 2009, and 567.6 million passengers used the U-Bahn in 2011, which declined to 428.8 million passengers in 2013. The network is undergoing expansion and rolling stock renewal. Since 1969, 200 million euros have been invested annually in the extension of the Vienna U-Bahn.