The Cross-Harbour Tunnel, which opened in 1972, is Hong Kong's first vehicular tunnel, providing a vital road connection between Hong Kong Island and Kowloon. Spanning a total length of 1.86 kilometers, it consists of two steel road tunnels, each featuring with two lanes, constructed using the single-shell immersed tube method. Since its opening, the Cross-Harbour Tunnel has remained the busiest and most frequently used tunnel in Hong Kong, with an average daily traffic volume of over one hundred thousand vehicles.