Taipei Metro Line 4

Zhonghe–Xinlu Line
Dingxi Station of TRTS Yellow Line
Overview
Other name(s)	Orange Line
Type	Rapid transit
Status	In service
Locale	Taipei and New Taipei, Taiwan
Termini	Luzhou, Huilong Nanshijiao
Stations	27
Services	Zhonghe Line, Xinzhuang Line, Luzhou Line
Operation
Opened	Zhonghe Line:   December 24, 1998 Luzhou Line:   November 3, 2010 Xinzhuang Line:   November 3, 2010 (Taipei City part) January 5, 2012 (Part of New Taipei City part)
Operator(s)	Taipei Rapid Transit Corporation
Rolling stock	Kawasaki C371 stock
Technical
Line length	31.5 km
Track gauge	1,435 mm (4 ft 8 1⁄2 in)
Electrification	Third rail (750 volts DC)
Operating speed	80 km/h
Route map

Zhonghe–Xinlu Line or Orange Line (O as identifier) is a line of Taipei Metro. As of 29 June 2013, all construction on the Line O has been completed. The line runs through New Taipei and Taipei and has a terminus in Taoyuan City.

Due to heavy traffic for residents in the districts of Luzhou and Sanchong traveling in and out of downtown Taipei, a rapid transit line was constructed to meet this urgent need. Although the Luzhou Line is technically only the section from Daqiaotou to Luzhou, the Xinzhuang Line section is commonly included as part of the Luzhou Line. All stations are equipped with platform screen doors and it is the first high-capacity line in the system equipped with them.

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

On 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.

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

On January 15, 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. 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. However, this did not occur. The section opened for service on September 30, 2012 along with Dongmen Station.