Coloured magenta on the MTR map, the line ran from Tuen Mun to Hung Hom, with a total length of 35.7 kilometres (22.2 mi), in 37 minutes.

[3] The railway connected the urban area of Kowloon and the new towns of Yuen Long, Tin Shui Wai and Tuen Mun in the northwestern New Territories.

A railway to the northwestern New Territories from the urban area in Kowloon was recommended as early as 1978 in a Tuen Mun Transport Study by Scott Wilson Kirkpatrick & Partner;[7] by the early 1990s, the surge of commuter towns in Yuen Long and Tuen Mun had frequently brought road networks to a standstill, as urban populations spilled over to the bedroom communities while keeping their jobs in Kowloon and Hong Kong Island.

Along with the Light Rail network, which was reconfigured as a feeder system, the new railway was designed to serve 1.08 million residents in northwestern New Territories, 25% of whom lived within walking distance to stations compared to 80% along the Tseung Kwan O line.[9]p.

[14] Frequent breakdowns (by local standards: 24 incidents in 2004 caused a delay of eight minutes or more)[15] led KCRC Chairman Michael Tien to announce that he would consider resigning if service performance failed to improve.

The track then runs northwest through a sealed box tunnel just to the north to and under the West Kowloon Highway through Lai Chi Kok Park into Mei Foo station, which has a ground-level/underground hybrid design.

The line emerges into open air just south of the train depot at Pat Heung and initially runs at-grade, and later on an embankment, as it approaches Kam Sheung Road station.

[19] Up to 26 sets run during the morning peak service with a 171-second headway; MTRC specifies capacities of 52 seated and 286 standing passengers per car.

[9] Crowding on trains–or a lack thereof–has been a matter of heated public debate since its inauguration, as the government has no specific indicator for measuring crowdedness in train compartments as of 2014.

[27] In industry journals, KCRC engineers and academics quoted ultimate limits upwards of 100,000 under 105-second headways,[8][9] in nine-car configuration; however, both post-merger MTRC[3] and government planning consultants report that the 'designed maximum one-hour carrying capacity' is actually 64,000, a figure described in Hansard footnotes as 'calculated in terms of the highest train frequency allowed with the existing signaling system';[28] in the consultants' report, 2011 average loading from Kam Sheung Road to Tsuen Wan West during the busiest morning peak hour stood at 65% (of the "one-direction passenger capacity of the trains operated along the railway line", the exact figure of which was unspecified):[29] consultants thus referred to "under-utilisation of train capacity"[29]3.11.

In present operations, parliamentary briefs state that the Kowloon Southern Link raised the one-hour carrying capacity from 39,900 to 46,900 pax/hr when headway was shortened from 3.5 minutes to 3.

In December 2013, the Transport and Housing Bureau submitted detailed definitions to legislators regarding average train loading without specifying the figures:[33] they were eventually released in February 2014[34] in a Legco subcommittee submission.

Around 650 passengers had to evacuate through the dark tunnel to the station, while around 340 people returned to the ground through a ventilation shaft at Chai Wan Kok.

[40] On the night of 21 July 2019, during ongoing protests in the territory, Yuen Long station was stormed by armed men, and 45 people were injured.