The Cross-Harbour Tunnel (abbreviated CHT or XHT) is the first tunnel in Hong Kong built underwater. It consists of two steel road tunnels each with two lanes constructed using the single shell immersed tube method.
It is the earliest of three vehicular harbour crossings in Hong Kong, opened for traffic on 2 August 1972. It was constructed under 30-year private-sector franchise based on a build–operate–transfer model, and title passed to the Hong Kong government in August 1999 upon termination of the franchise. It has become one of the most congested roads (mainly towards the Hong Kong Island direction) in Hong Kong and the world, with 116,753 daily vehicles in 2013.
The Hong Kong government used the operator model "Build Operate Transfer", or "BOT", for the implementation of the tunnel project; Financing and construction was the responsibility of a private enterprise, which was granted a concession to operate and collect tolls for 30 years. The concession was given to the then Cross-Harbor Tunnel Company Limited (香港 隧道 有限公司), today: Cross Harbor Holdings Limited (港 通 控股 有限公司), which was founded in 1965 to carry out the tunnel project. The Hong Kong government participated to 20% in order not to fully hand over their influence on the project. The tunnel was designed with two lanes for each direction of travel for a capacity of 80,000 vehicles. The project was structurally managed jointly by the British engineering firms Scott Wilson Kirkpatrick & Partners and Freeman Fox & Partners. The tunnel links the main financial and commercial districts on both sides of Victoria Harbour, connecting Kellett Island (a former island now connected to Hong Kong Island by reclamation), with a reclaimed site at Hung Hom Bay, Kowloon. The toll plaza is located at the Hung Hom end of the tunnel, and has 14 toll booths. It provides the first road link between Kowloon and Hong Kong Island. Prior to the opening of the tunnel, cross-harbour vehicular traffic depended on ferries and for passengers, the Star Ferry. The project was joint-engineered by Scott Wilson Kirkpatrick & Partners and Freeman Fox & Partners 
Construction began in September 1969 and was to last four years. The concession period already ran from the start of construction, so that the operator carried out the construction one year faster than planned. On 2 August 1972, the tunnel was opened for traffic and cost 5 HK $ per car for transit. After just three and a half years of operation, the operator had re-recorded the construction costs.
In 1984, the Hong Kong government introduced a tax in addition to the operator's toll to make the overcrowded tunnel less priced. The price for a car transit was now 10 HK $.
In 1993, an electronic toll collection system was installed. Together with measures to control the flow of traffic, the vehicle capacity could be increased.
It was administered by The Cross-Harbour Tunnel Company Ltd until August 1999, when the operation franchise agreement expired and the government assumed control. Since 1 November 2010, the tunnel is managed, operated and maintained by Serco on contract basis.
|Initial (1972)||from 1984||from 1992||from 1999|
|Light goods vehicle (LGV)||$10||$15||$15||$15|
|Heavy goods vehicle (HGV)||$20||$25||$30||$30|
|source: Consultancy report|
The tunnel generates approximately HK$700 million in annual toll revenue.
As of 2018[update], there are 44 bus routes passing through the tunnel.
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