an M car is 3. This digit then follows the three digits of the set number. For example, C301 set 001/002 consists of carriages 1001-2001-3001+3002-2002-1002. A single set cannot be in revenue service except C371 single sets 397–399, where their M car is exactly a DM car despite its first digit being 3. These single sets run exclusively on the Xinbeitou and Xiaobitan branch lines. Before the C371 single sets were in revenue service on 22 July 2006, the M cars of C301 sets 013/014 were converted to temporary cab cars to run the Xinbeitou branch. In 2010, the new C381 was built for Taipei Metro to cope with increasing passenger ridership and the expansion of its network route. Upon entering service on 7 October 2012, three C381 trainsets are servicing the Beitou – Taipower Building segment of the Tamsui and Xindian Lines, with the remaining fleet being put into service on 20 October 2012. These trains provided much-needed capacity increase when the Xinyi and Songshan extensions opened in late 2013. After November 2014, the C381 trains are serving both and . Whereas the earlier heavy capacity train types have largely retained the same design, the C381 sets are more distinctive with double blue stripes and the re-positioning of the logo from the driver's door to well below the passenger's windows, right on the stripe. Also placed were the more "sleeker" cab and the new advertising screens (as seen in newer Japanese commuter trains such as the E233 series) to improve energy efficiency, although it retains the same propulsion as the C371s. Fleet roster Medium-capacity fleet Heavy-capacity fleet Engineering trains Taipei Metro also uses a fleet of specialised trains for maintenance of way purposes: Depots The system currently has 10 depots, with more under construction. Reception Taipei Metro is one of the most expensive rapid transit systems ever constructed, with phase one of the system costing US$18 billion and phase two estimated to have cost US$13.8 billion. Despite earlier controversy, by the time the first phase of construction was completed in 2000, it was generally agreed that the metro project was a success, and it has since become an essential part of life in Taipei. The system has been effective in reducing traffic congestion in the city and has spurred the revival of satellite towns (like Tamsui) and development of new areas (like Nangang). The system has also helped to