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 in 1972. It was constructed under a 30-year private-sector franchise based on a build–operate–transfer model, and the title passed to the Hong Kong government in 1999 upon termination of the franchise. It has become one of the most congested roads in Hong Kong and the world, with 116,753 vehicles passing through it daily in 2013. History 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-Harbour Tunnel Company Limited (), today the Cross-Harbour Holdings Limited (), 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 on the western side of Hung Hom Bay, Kowloon, off then Hong Kong Technical College. The toll plaza is located at the Hung Hom end of the tunnel, and has 14 toll booths. It provides the first road link and the first link for land transport 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 ran from the start of construction, and the operator accordingly completed the construction one year faster than planned. On 2 August 1972, the tunnel was opened for traffic, charging HK$5 per