a treaty with the Taipei Transit Council (TTC), composed of three American consultant firms, to do overall research on a rapid transit system in metropolitan Taipei. Apart from adjustments made to the initial proposal, Wenhu line of the medium-capacity metro system was also included into the network. In 1986, the initial network design of the Taipei Metro by the CEPD was passed by the Executive Yuan, although the network corridors were not yet set. A budget of NT$441.7 billion was allocated for the project. On 27 June 1986, the Preparatory Office of Rapid Transit Systems was created, which on 23 February 1987 was formally established as the Department of Rapid Transit Systems (DORTS) for the task of handling, planning, design, and construction of the system. Apart from preparing for the construction of the metro system, DORTS also made small changes to the metro corridor. The 6 lines proposed on the initial network were: Tamsui line and Xindian line (Lines U1 and U2), Zhonghe Line (Line U3), Nangang Line and Banqiao Line (Line S1), and Muzha (now Wenhu) line (Wenhu line medium-capacity), totaling 79 stations and route length, including of elevated rail, at ground level, and underground. The Neihu Line corridor was approved later in 1990. On 27 June 1994, the Taipei Rapid Transit Corporation (TRTC) was formed to oversee the operation of the Taipei Metro system. The Executive Yuan approved the initial network plan for the system on 27 May 1986. Ground was broken and construction began on 15 December 1988. The growing traffic problems of the time, compounded by road closures due to TRTS construction led to what became popularly known as the "dark age of Taipei traffic". The TRTS was the center of political controversy during its construction and shortly after the opening of its first line in 1996 due to incidents such as computer malfunction during a thunderstorm, alleged structural problems in some elevated segments, budget overruns, and fare prices. Opening and Initial network The system opened on 28 March 1996, with the elevated , a driverless, medium-capacity line with twelve stations running from to . The first high-capacity line, the , began service on 28 March 1997, running from to , then extended to at the end of the year. On 23 December 1998, the system passed the milestone of 100 million passengers. 1999–2006 Expansions On 24 December 1999, a section of the was opened between