Zhonghe–Xinlu line

In June 1992, the construction of Zhonghe Line began. It was the most difficult and arduous one among all lines of Taipei metro. The tunnels running through Zhonghe-Yonghe area had to pass under narrow streets, skyscrapers and crowded blocks, with limited spaces for underground station above ground. As a result, the whole neighborhood traffic had its so-called "Dark Ages" when the cut-and-cover method was used for station platforms, concourses and crossovers during the 1990s. Besides the river-crossing section, the work suffered from biogas below the waterfront. After the construction, Zhonghe Line became more costly than all the other lines, 6,249 million NT dollars per kilometer.[2]

Since the line opened for service on 24 December 1998, it has been the most important access to downtown Taipei for nearly half a million of commuters who live in the district.

On 15 January 2011, Dongmen Station was still under construction while the track for the section from Zhongxiao Xinsheng to Guting (which passes through Dongmen Station) had already been laid.[3] At the time, Taipei Rapid Transit Corporation Vice Bureau Chief Chang Pei-yi noted that there was a possibility of opening the line for service while skipping both Dongmen and Guting stations, thus allowing for through service on the Orange Line.[3] However, this did not occur. The section opened for service on 30 September 2012 along with Dongmen Station.

On 18 December 2011, the 8.2 km (5.1 mi) Daqiaotou to Fu Jen University section passed final inspections by the Ministry of Transportation and Communications.[4] It opened for service on 5 January 2012.[5] On its first full day of service, the line served 82,000 passengers.[6] The line is expected to serve 100,000 passengers daily.

As of April 2016, the Xinzhuang Depot was still under construction and expected to be finished in January 2018, completing the Xinzhuang Line.[7]

Although the line was called the Luzhou Branch Line during construction, the name was changed to simply the Luzhou Line before it opened for service.

• 2002: The Luzhou and Xinzhuang lines begin construction as part of Phase II development of the Taipei Metro.[8]
• September 2007: Track laying begins for the Luzhou Line.
• 25 September 2008: Since track laying has been completed for the Luzhou Line, tracks are laid for the segment of the Xinzhuang Line within Taipei.
• 1 April 2009: Train testing begins for the Luzhou Line and the segment of the Xinzhuang Line within Taipei.
• 22 August 2009: It is announced that although the line was to come into operation before the Spring Festival of 2010, due to malfunctions in the Neihu Line, service for the line would be pushed back to September 2010.[9]
• 24 April 2009: The Department of Rapid Transit Systems (DORTS) denies saying that the line would open before the Spring Festival in 2010. The Executive Yuan sets the line to begin service by 31 December 2010. DORTS says it will push forward with an anticipated September 2010 opening date.[10]
• 2 March 2010: DORTS says that the line is planned to open by 1 September 2010 in order to coincide with the Flora Expo. It will use the Taoyuan International Airport MRT's power as backup, so that by November 2010 the Xinzhuang Line can begin train testing through Touqianzhuang.[10]
• May 2010: Construction for Sanchong Elementary School, Sanhe Junior High School, Luzhou, and Luzhou Depot is completed. Construction for Sanmin Senior High School and St. Ignatius High School is finishing up.
• 30 June 2010: Construction finishes on all stations.
• July 2010: Train testing begins.
• September 4–5, 2010: The Luzhou Line and Xinzhuang Line city portion (to Zhongxiao Xinsheng) undergoes initial public testing.[11]
• 3 November 2010: The line opens for service with the opening of the Luzhou to Zhongxiao Xinsheng section.[12] A free trial period for the line ran until 2 December 2010.[8]
• 3 December 2010: The line began revenue service.[8]

Since its first three weeks after opening, the line (along with the Xinzhuang Line section) had reached a total ridership of over 3 million passengers, with an average of 157,000 passengers per day.[13] It is expected to cut travel time between Luzhou and Taipei by at least half,[14] with travel time between Luzhou and Taipei Main Station cut down to 17 minutes.[15] The system surpassed an annual ridership of 500 million for the first time on 29 December 2010, widely attributed to the opening of the new line.[16] The line has been effective in relieving congestion, with a 24% increase in average vehicle speed crossing Taipei Bridge (to Taipei) during rush hour since the opening of the line.[17] During the initial one-month trial, bus routes that ran parallel to the metro route experienced a 40% decrease in ridership, although bus ridership is expected to rise again after the end of the free trial.[18]

In anticipation of the opening of the new line, property prices along the route have risen by 36% since 2008.[19] Although small businesses along the line (most notably in Zhongshan and Datong, two older districts) have benefited from increased business during the free trial period, analysts noted that the initial business boon may only be short-lived and it may be years before these areas see real benefits as a result of the new line.[20]

Over the years, three versions of rolling stock were used on this line, as well as on the through services between Nanshijiao and Beitou. Originally, the line used a large fleet of C301 train sets. In 1999, only a few C341 train sets were used. In 2007, some C371 train sets were introduced. Today, the entire fleet used on this line is the C371 train sets after the original C301 train sets were confined to the Tamsui and Xindian Lines upon the opening of Dongmen Station on 30 September 2012.

As of December 2017, the typical off-peak service is:

• 7 trains per hour (tph) between Huilong and Nanshijiao
• 7 tph between Luzhou and Nanshijiao