The Tuen Ma line () is a rapid transit line that forms part of the Mass Transit Railway (MTR) system in Hong Kong. Coloured brown on the map, the Tuen Ma line is in length, making it the longest line of the MTR network. It has a total of 27 stations, more than any other in the MTR system. The Tuen Ma line is a merger of the two former MTR lines, the West Rail line and the Ma On Shan line, via a new stretch of mostly-underground railway known as the "Tai Wai to Hung Hom section" () of the Sha Tin to Central Link project, consisting of of track and six new intermediate stations. The Tai Wai to Kai Tak section (大圍至啟德段) opened on 14 February 2020, while the Kai Tak to Hung Hom section opened on 27 June 2021, thereby completing the line. During the planning and construction phase, this line was referred to as the "East West Corridor" (). On 25 May 2018, the finalised name "Tuen Ma line" was confirmed by the MTR Corporation, reflecting the termini of the full line, namely Tuen Mun and Ma On Shan. The full journey time is about 73 minutes.<ref> Overview The line presently starts at Tuen Mun station, Tuen Mun and ends at in Wu Kai Sha, Ma On Shan. It is long with 27 stations, and a complete journey lasts 73 minutes in either direction. There are six interchange stations: and with the , and with the , with the and with the . The line has 2 maintenance depots at Tai Wai and Pat Heung. Like all MTR lines, the Tuen Ma line is grade-separated throughout its entire length. It is mainly underground in the urban sections of Kowloon and Tsuen Wan, and at-grade or elevated in the rest of the New Territories. Most of the original Ma On Shan line (between Tai Wai and Wu Kai Sha) is built on a viaduct on land which had been reserved for the purpose of a railway from the outset of the development of Ma On Shan New Town. However, the section between and is at ground level, located between the carriageways of Tate's Cairn Highway, along with the section between Tai Wai to , which is also partially on an embankment and parallel to the . The line then goes underground through Diamond Hill station and Kowloon