MTR
When service of this line started, the section of the Kwun Tong Line from Chater to Argyle, present-day Mong Kok station, was transferred to the Tsuen Wan Line. Thus, Waterloo became the terminus of the Kwun Tong Line, and both Argyle and Prince Edward stations became interchange stations. This change was made because system planners expected traffic of the Tsuen Wan Line would exceed that of the Kwun Tong Line. This forecast proved quite accurate, necessitating a bypass from the northwestern New Territories to Hong Kong Island. Launched in 1998, the Tung Chung Line serves exactly that purpose.