Four lanes of roadway will pass in stacked upper and lower decks through 3.3 miles (5.4km) of tunnel. This includes a 45 foot diameter (13.7 metre) bored submarine tunnel over 2 miles (3.4km) long and twin New Austrian Tunnelling Method (NATM) tunnels, each 0.6 miles (1 km). At depths of 330 feet (100m) below the water surface, in sand and gravel, the single pass segmental lining will be required to resist 11 bars of water pressure and large seismic forces. Construction also requires tunnelling through poor quality rock at both the Asian and European sides of the crossing, and mixed-face conditions beneath the Bosphorus. Special attention had to be given to design of the bored tunnel lining segments, gaskets, and bolted connections.
The significant technical challenges faced by the designers and builders are coupled with both obstacles and opportunities brought together by the multinational design and construction teams. The design and construction coordination was accomplished with support by staff in Turkey, Korea, Great Britain, Austria, and the United States. The construction drawings were bilingual, Turkish and English; and the design was required to meet Turkish, European, and American codes.