TEMPO.CO, Jakarta - An underwater tunnel or toll road is a highway below sea level that provides access for vehicles from one land to another. The underwater toll road has a long history, starting from a road that "merely" crossed a river of 0.4 kilometers wide to an underwater toll road with a length of more than 50 kilometers.

Undersea toll roads can now be found in several developed countries. Indonesia plans to build an underwater toll road in the new capital city of Nusantara, or IKN. In the future, the underwater toll road will connect the Balikpapan-Samarinda toll road with the new capital.

Here is the list of countries that own an underwater toll road:

  1. China

In January 2022, China officially inaugurated another of its underwater toll roads measuring 10.79 kilometers. The toll road is called Taihu Tunnel as it spans in the middle of Lake Taihu in Jiangsu Province. Previously, China built an undersea tunnel in Xiamen, Fujian Province 2005–2010, called the Xiang’an Tunnel of 8.69 kilometers long.

Another one connects Hong Kong, Zhuhai, and Macau which is a combination of bridge and underwater tunnel. The length of the underwater road is 6.7 kilometers from the overall total of 55 kilometers long.

  1. Britain

Britain has the oldest underwater tunnels, namely the Blackwall Tunnel, the Queensway Tunnel, and the Channel Tunnel.

The Blackwall has two separated lines with lengths of 1.35 kilometers and 1.17 kilometers respectively. The roads lie under the Thames River in the Blackwall and Greenwich areas since 1897.

The Queensway Tunnel was built in 1925–1934 under the Mersey River between Liverpool and Birkenhead. The road also known as the “Birkenhead Tunnel” or the “Old Tunnel” measures 3.24 kilometers long.

Meanwhile, The Channel Tunnel lies from Folkestone, the U.K. to Calais, France with the underwater line at 37.9 kilometers from the total of 50.4 kilometers. The road was built in 1988–1994.

  1. Japan

Japan has at least two underwater roads, which are the Kanmon Tunnel and the Tokyo Bay Aqua-Line. The Kanmon Tunnel connects the islands of Honshu and Kyushu in the cities of Shimonoseki and Kitakyushu. The length is 3.46 kilometers which is equipped with sidewalks for pedestrians. The tunnel was built from 1937 to 1958.

Meanwhile, the Tokyo Bay Aqua-Line is a combination of a bridge and an undersea tunnel. It is located under Tokyo Bay with a length of 9.6 kilometers from a total of 23.7 kilometers.