Work has started on a geological condition field study for a proposed 6.5km three-deck road and rail tunnel under the Bosporus Strait in Istanbul, Turkey.
Average daily road traffic through the Great Istanbul Tunnel is expected to be 120,000 vehicles and the rail line will move around 75,000 people daily.
The tunnel, announced in 2015, will be nearly 19m in diameter and have two road levels and one rail level. It will run between Gayrettepe on the European side and Küçüksu on the Asian side.
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