Third Bridge on Bosphorus

The Third Bosphorus Bridge, the widest suspension bridge, as well as the bridge with the tallest pylons, at a global level,  forms part of the North Marmara Highway project. The project has the twin goal of relieving traffic congestion and of creating a corridor that facilitates commercial traffic from and to Greece. The bridge is located to the north of the Bosphorus Strait, just before the Black Sea and will connect Poyrazkoy on the Asian side to Garipce on the European side.

The contract involves the construction of a cable-stayed suspension bridge with a central span measuring 1,408 metres in length. The load-bearing structure that will support the stays and suspension cables, which the bridge's spans are secured to, comprises two A-shaped pylons, each built using a pair of triangular-section leaning pillars. The two main concrete and steel pylons have their foundations in the earth on the banks of the strait and will stand 318 metres above the level of the water. 

The widest deck in the world comprises two 4-lane carriageways, each separated by a central, twin-track railway corridor, for a total width of 59 metres. The planned transit speed is 120 km/h for road traffic, 160 km/h for passenger trains and 80 km/h for freight trains.  The bridge will also be accessible to pedestrians thanks to two walkways built along the external edges of the deck, with a width of 2.5 metres. 

The central span stretches between the two tallest A-shaped pylons in the world (318 m) and is built of steel with segments measuring 24 metres in length and weighing 840 tons each. While the two side spans, approach viaducts and anchor block will be made of concrete. 

The following are planned to build the bridge: the use of 241,000 m³ of concrete, 65,000 tons of steel for structure, 31,000 tons of steel for reinforcement, and 29,000 tons for pre-stressed parts, as well as the movement of 897,000 m³ of earth and 32,000 m³ of ground fill. 

The design has taken into account the possibility of major-intensity earthquakes occurring given that the site area is affected by the Anatolian fault which runs from east to west along the northern part of Turkey up to the Marmara sea. A preliminary study was carried out in accordance with the guidelines set forth in AASHTO standards (American Association of State Highway and Transportation Officials) for bridge design. 

The work is being performed using the BOT formula (Build-Operate-Transfer) with regard to design, performance and subsequent management of the project funded on a project finance basis.