Also, a new network of bus services in the Favoriten area commenced. From the same date tram lines 2, 10, 44 and 60 saw major changes and Line 58 was replaced by extensions of lines 10 and 60. As of September 2017, the following lines operate: The longest line is currently line 6, running from the U-Bahn station at Burggasse-Stadthalle to Kaiserebersdorf. On the other hand, the shortest one is line 42 running only . The Vienna tram fleet consists of both high-floor and low-floor vehicles. On weekdays, some lines operate with a combination of high and low-floor trams, but on weekends (especially Sundays), only a limited number of high-floor trams are used on lines D, 2, 5, 25, 31, 38 and VRT. Low-floor trams were successively introduced from 1995, most recently on line 33 in September 2011. This allowed all tram stops in Vienna to be served by such vehicles, thus providing step-free travel throughout the entire network. From 1959, articulated tramcars of Type E were used. However, it became difficult to operate these trams with trailer cars due to their underpowered motors, necessitating their replacements soon afterwards. The successors, the Type E1 trams, were first delivered in 1966. They were of similar appearance to their predecessors, but equipped with more powerful motors. The Type E remained in service until 2007, most recently on lines 10 and 62. After production of the E1 ceased in 1976, a further successor generation, the Type E2, was developed, and has been in service since 1978. The trailer fleet constructed to match the tramcars is made up of Types c4 for the E1 tramcars, and Type c5 for E2 tramcars. On less frequented lines, the tramcars also operated without trailers. Following a number of serious accidents, the majority of the high-floor trams have been fitted with electric door edge sensors and rear-view mirrors. The articulated Ultra Low Floor (ULF) trams, built by a consortium composed of Siemens and ELIN, come in two lengths: Type A, a short version with five sections, and Type B, a longer, seven-section version. Since 1995, one prototype of each length operated on the network. Since 1997, series production versions of both types have been in service. Type A1, a further development of Type A, has been in service since 2007 as the first generation of Vienna tramcars to be fitted with air conditioning.