The Bannan or Blue line (code BL) is a metro line in Taipei operated by Taipei Metro with a total of 23 stations serving the districts of Nangang, Xinyi, Daan, Zhongshan, Wanhua, Banqiao and Tucheng. The line's name is a portmanteau of Banqiao and Nangang. The entire line runs underground. The excavation of tunnels using the cut-and-cover method resulted in large scale detouring of road traffic. Because of that, the line runs beneath existing roads and totals 28.3 km (17.6 mi).