the tracks with the U1 from Westfriedhof to Kolumbusplatz, the U2 from München Hauptbahnhof to Innsbrucker Ring, and the U5 from Innsbrucker Ring to its southern terminus Neuperlach Zentrum. The stations along U7 line are Westfriedhof, Gern, Rotkreuzplatz, Maillingerstraße, Stiglmaierplatz, München Hauptbahnhof, Sendlinger Tor, Fraunhoferstraße, Kolumbusplatz, Silberhornstraße, Untersbergstraße, Giesing Bahnhof, Karl-Preis-Platz, Innsbrucker Ring, Michaelibad, Quiddestraße, and Neuperlach Zentrum. U8 This booster line started operations in December 2013. It only operates on Saturday afternoons. The U8 begins in the north at Olympiazentrum and shares the tracks with the U3 as far as Scheidplatz, where it continues along the U2 tracks to München Hauptbahnhof and terminates at Sendlinger Tor. It is only running on Saturdays to ease crowding on the U2 and U3 lines, and to provide people an easier access to the Olympic Park from Munich Central Station. The stations along U8 line are Olympiazentrum, Petuelring, Scheidplatz, Hohenzollernplatz, Josephsplatz, Theresienstraße, Königsplatz, München Hauptbahnhof, and Sendlinger Tor. Rolling stock Munich U-Bahn uses three different generations of electric multiple unit trains. The stock of over 550 carriages is shared between all lines. Class A Class A trains were built between 1967 (prototypes) and 1983. The units consist of two carriages, which always remain coupled in normal operation. The double-carriage units have a length of , a height of , and a width of . Each unit has three doors per side and a capacity of 98 seats and standing room for 192 passengers. A total of 193 double-carriage units were delivered, of which 179 are still in use in Munich. Up to three A two-carriage units can be coupled together to form a 3/3 train (Langzug). Class B Class B trains were built between 1981 and 1994 to provide more stock to service the growing network in the 1980s. As with the class A trains, six prototypes were ordered. However, it took six years until the series production started and the prototypes had to be modified to match the series-production units. B units have the same size as A units but differ in the design (especially of the front window) and use three-phase current instead of direct current motors. The other difference is the door opening mechanism. On B units, the passengers only need to pull just one handle to open both door leaves rather than both handles as on A units. Of a total of 63 units, 57 are still in service