More than 150 years since it was first dreamed up by an Ottoman sultan, Turkey on October 29 unveiled the world's first sea tunnel linking two continents. The tunnel, which has taken nine years to construct under the Bosporus straits, is part of Istanbul's metro service, and will connect the European and Asian sides of Turkey's biggest city. Known as the Marmaray metro link, it is slated to revolutionize the city, where public transport is limited and traffic jams are the stuff of legend. First suggested by Ottoman sultan Abdoul Medjid in 1860, it wasn't until 2004 that Erdogan - then Mayor of Istanbul - gave the final go-ahead for the tunnel, as part of a series of lavish construction projects for the city including a third airport, a parallel canal and a third bridge. Nine years after Erdogan gave it the green light, the US$ 4.6 billion first stage of the Marmaray project is now opened - four years behind schedule. Presenting something of a technical challenge, the 1.4 kilometer long undersea tunnel was constructed by lowering steel-lined pre-cast concrete sections into a trench excavated 60 meter down on the seabed of the Sea of Marmara, where they were then buried. A further 12.2 kilometer of on-land tunnels connect the three stations which make up the project's first phase. The rail tunnel is said to be earthquake-proof, an important consideration in an area plagued by strong seismic activity.

China will invest US$ 42 billion, to revive a long-stalled plan to build the world's longest undersea tunnel across the Bohai Strait linking the country's eastern and northeastern regions. Deep beneath the Bohai Sea, Chinese engineers may soon begin boring the longest submarine tunnel on the planet. At an estimated 123 kilometers long, it would surpass the combined length of world's two longest underwater tunnels-Japan's Seikan Tunnel and the Channel Tunnel between the UK and France. The tunnel will run from the port city of Dalian in northeastern Liaoning province to Yantai city in eastern Shandong. Today the drive between Dalian and Yantai takes around seven to eight hours. The Bohai Tunnel would shorten that to an hour. China announced plans in 1994 to build the tunnel, at a cost of US$ 10 billion, and set to be completed before 2010. But more than 20 years on, the project remains stuck in the planning stage without elaborating. Currently world's longest undersea tunnel is in Japan. The 54 kilometer Seikan tunnel links Honshu and Hokkaido islands and started operating in 1988 after more than two decades of construction. The Channel tunnel between England and France is about 51 kilometer long.

The Norwegian Government has revealed plans for the construction of the world's first ship tunnel through a mountain to help ships navigate a dangerous section of the country's south-western coast. The government has agreed to provide US$ 274 million for the Stad Ship Tunnel, which will be built to a height of 45 meters, width of 36 meters and will span a length of 1.7 kilometers. The proposed tunnel, which is being planned by Nordfjord Vekst, would bypass the Stadlandet (Stad) peninsula in Selje, Norway linking two fjords near the towns of Teigen and Berstad. Peaking at 645 meters, the Stad peninsula is a mountainous divide between the Norwegian Sea to the north and the North Sea to the south. The project is being proposed to reduce navigation on the existing shipping route, which exposes vessels to some of Norway's most dangerous waters, where currents and waves come from different directions, which has contributed to 46 accidents and near-accidents since 1945. The Stad Ship Tunnel would be the world's first shipping tunnel capable of accommodating large cargo and passenger vessels of up to 16 thousand tons. Royal Academy of Engineering associate Robert Benaim told the BBC that the project would include the construction of a cofferdam at either end of the tunnel to keep the water out until excavation is complete. Nordfjod Vekst project director Randi Homborstad said: "As the sea is the backbone of transport along the west coast of Norway, public transport could be upgraded with improved regularity in cargo services and a new year-round high-speed passenger ferry service between the coastal cities of Bergen and Alesund." Construction of the new tunnel is expected to commence in 2018 and would take around four years to complete.

As reported news agency Xinhua, construction of a tunnel that will traverse Trola Mountain in southwestern Sichuan Province began on June 1. At an altitude of 4.24 to 4.38 kilometers, the Trola Mountain tunnel will be the world's highest on a highway. As part of Sichuan-Tibet Highway that links Chengdu, Sichuan in the east with Lhasa, Tibet in the west. The 7-kilometers tunnel will shorten travel time across the mountain from more than two hours to only about 10 minutes, construction manager Li Ming said. He also added that, workers must first build an approach that is 14.06 kilometers long on the east side of the mountain. The tunnel is scheduled to be completed in four years with an investment of $US173 million. The 2,415 thousand kilometers Sichuan-Tibet highway is considered one the world's most deadly as it traverses a dozen rivers and 14 mountains with altitudes of 4 to 5 kilometers. China has spent nearly $ US 21.6 billion on development of 188 key projects in Tibet between 2005 and 2010, and key among them are projects that link Tibet to the rest of China. And the governments of Sichuan and Tibet are planning to build more tunnels on several key mountains to improve traffic.