By 2028, millions of people will be able to travel between Europe and Asia through an underwater tunnel costing approximately $4 billion (£3.1 billion).
The Great Istanbul Tunnel, a four-mile-long multi-purpose underwater structure, will cross the Bosphorus Strait in Istanbul, Turkey. This natural waterway connects the Black Sea to the Sea of Marmara and serves as a continental boundary between Europe and Asia.
The tunnel will consist of three levels: two dedicated to road traffic and one for a rail system.
With a diameter of 19 meters, it will be located 110 meters below sea level. The tunnel will connect highways linking Istanbul’s three major airports—Atatürk, Sabiha Gökçen, and Istanbul Airport.
The railway section of the Great Istanbul Tunnel will include 13 stations and will have the capacity to transport 70,000 passengers per hour in a single direction.
The tunnel will also connect with 11 other railways and enable the Metrobus line, an essential part of Istanbul’s transportation system, to operate at optimal capacity.
On May 10, Turkey’s Transport and Infrastructure Minister Adil Karaismailoğlu provided an update on the project. He confirmed the timeline for the opening of the combined highway and railway tunnel, which is expected to be the world’s longest underwater tunnel.
Karaismailoğlu stated that the tunnel will reduce rail travel times across the Bosphorus to just over 40 minutes.
The project is considered crucial for the region. According to Istanbul’s transportation plan, daily crossings between the European and Asian sides of the river are projected to exceed three million in the future, a significant rise from the current two million.
The project is being built using one of the world’s largest tunnel-boring machines (TBM), which is 83 meters long and 20 meters wide.
This will be the third tunnel under the Bosphorus, following the Marmaray Tunnel (2 miles) and the Eurasia Tunnel (3.3 miles). Turkey’s Transport Minister Adil Karaismailoğlu confirmed the tunnel will be the world’s longest underwater tunnel, although Denmark and Germany’s 11-mile Fehmarnbelt Tunnel (set to open in 2029) will surpass it in length.
The Great Istanbul Tunnel is a critical project for Istanbul’s future, aiming to ease congestion and enhance connectivity across this vibrant city.