The line partly uses a former air-defence evacuation tunnel built during the Second World War. Line 1 is 17.5km long with 18 underground stations and links the city's East and South mainline stations via the city centre.\r\nEach train, which comprises four motored cars and two trailers, has an aluminium alloy car body and is mounted on CW2100 bogies. Bombardier supplied the traction and auxiliary systems as well as the train control equipment.\r\nThe trains have sliding pocket doors, environmentally-friendly high-voltage ac (HVAC), air purification, an intelligent real-time information display, and a passenger information system.\r\nTwo more lines are planned. Line 2 will run from the northwest via the city centre to the eastern suburbs, while Line 3 will encircle the city centre. Two further lines are proposed to create a 143km network.