color is red. Line 2 Line 2, a monorail line, runs and has 25 stations. It begins as a subway under downtown Jiefangbei, then runs west along the southern bank of Jialing River on an elevated line, and then turns south into the southwestern inner suburbs, looping back east, to terminate at Yudong, in Ba'nan District. It runs mostly elevated, but a section is underground, including three of its 18 stations in the Jiefangbei CBD and central Daping areas in the extremely-dense area of Yuzhong District. Line 2 runs through four administrative districts in the central city (Yuzhong, Jiulongpo, Dadukou, and Ba'nan). In 2010, Line 2 served 45 million passengers. It also runs through Daping CBD, Yangjiaping CBD in Jiulongpo District, and Chongqing Zoo at. Most trains have four cars, and six-car trains began to operate in September 2012. Line 2 is the first rapid transit line to open in the Interior West of China, in 2005. In 2013, six-car trains are being implemented because of overcrowding and increasing demand. Line 2's color is green. Line 3 Line 3 is the longest and busiest monorail in the world. It runs from north to south and links the districts separated by the Yangtze (Chang Jiang) and the Jialing Rivers. The initial segment, from Lianglukou to Yuanyang (18 stations, ), opened on 29 September 2011, with a northern extension, from Yuanyang to Jiangbei Airport, opening on 30 December 2011. A southern extension, from Ertang to Yudong, opened on 28 December 2012. Most trains have six cars, more than on the older Line 2. The line started to equip eight-car trains in 2014, which are now in operation. There are interchange stations in the Yuzhong district with Line 1, at Lianglukou (Caiyuanba Intercity Railway/Coach Station), and with Line 2, at . Line 3's color is indigo. Line 4 Line 4 is a rapid transit line. In June 2018, debugging of the first segment of Phase I commenced. The line began operating on 28 December that year. Line 4's color is orange. Line 5 Line 5 is a northeast–southwest heavy-rail line crossing the centre, and the line has opened its northern and southern sections of phase 1 and northern extension. It will connect Yubei, Jiangbei, Yuzhong, Jiulongpo, Shapingba and Dadukou districts. New six-car trains were introduced on the line. Line 5's color is light blue. Line 6 Line 6 is the second heavy-rail subway