Line BL of Taipei Metro (Bannan Line or Blue Line or Line 5) is a high-capacity rapid transit line comprises three sections: Nangang Section, Banqiao Section, and Tucheng Section. The lines are divided at Ximen Station and Fuzhong Station, and offer through traffic to one another. It has a total of 23 stations serving the Nangang, Xinyi, Daan, Zhonghsan, and Wanhua districts, as well as into the New Taipei districts of Banqiao and Tucheng.
The Banqiao and Nangang Sections are collectively called the Bannan Line. 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).
Service on this line is divided into a full-length service from Taipei Nangang Exhibition Center to Dingpu, as well as a shorter service from Taipei Nangang Exhibition Center but terminating at Far Eastern Hospital.
November 8, 1990: The Nangang Section begins construction.
December 30, 1991: The Taipei Main Station western underground passageway opens.
December 24, 1993: Nangang Section construction at the intersection of Zhongxiao East Rd. and Shaoxing Rd. caves in, causes traffic jams.
October 30, 1998: Construction is completed on the tunnel between Kunyang and Houshanpi.
December 24, 1999: The segment from Taipei City Hall to Longshan Temple begins revenue service.
August 31, 2000: The segment from Longshan Temple to Xinpu begins revenue service.
December 30, 2000: The segment from Kunyang to Taipei City Hall begins revenue service.
September 17, 2001: Typhoon Nari floods many Nangang Section stations, rendering them nonoperational.
November 29, 2001: Typhoon-damaged Taipei Main Station re-opens for service.
December 30, 2003: The Nangang Section eastern extension to Nangang begins construction.
November 17, 2004: The Nangang Section eastern extension to Taipei Nangang Exhibition Center begins construction.
May 27, 2006: The segment from Banqiao to Tucheng opens for trial operations.
May 31, 2006: The segment from Xinpu to Yongning begins revenue service.
May 16, 2008: The Nangang Section eastern extension to Nangang begins trial service.
December 25, 2008: The Nangang Section eastern extension to Nangang begins revenue service.
February 27, 2011: The rest of the Nangang Section eastern extension to Taipei Nangang Exhibition Center opened for service.
May 21, 2014: The 2014 Taipei Metro attack occurs between Longshan Temple and Jiangzicui when 21-year-old university student Cheng Chieh attacked passengers with a fruit knife, leading to 4 deaths and 24 injuries.
July 6, 2015: The Tucheng Section extension to Dingpu Station begins revenue service, the final expansion of the line.
Nangang, Banqiao, and Tucheng Sections connect through to each other. Service routes are divided into:
