The tunnel will provide a new strategic transport link between Europe and Asia, shortening the journey time between Kazlicesme and Goztepe from 100 minutes to just 15 minutes.
Turkish President Recep Tayyip Erdogan on Saturday took a test drive through a tunnel that connects Istanbul's Asian side to the European half under the Bosphorus.
The Eurasia Tunnel will open to the public on December 20 but Erdogan, accompanied by Prime Minister Binali Yildirim and Transport Minister Ahmet Arslan, made the first journey from the Asian side to the European side in a black car.
"Today, we conducted a final test drive through one of Turkey's historic projects," said Erdogan. "I will inaugurate it with my nation on December 20."
Once operational, the tunnel would cut travel time between the farthest destinations of Istanbul's two sides from around 100 minutes at present during rush hour to just 15.
According to the developers of the project, the tunnel would contribute to the economy by reducing fuel consumption, as well as carbon emission amounts.
"Istanbul is on the eve of acquiring another mega project," said Prime Minister Binali Yildirim, who was the transport minister when the project was launched.
"The Eurasia Tunnel is the deepest underwater passage ever built in the world," he added.
Over five kilometers of the project will comprise a two-story tunnel constructed underneath the seabed using special technology with approach tunnels constructed using other methods, said an official leading the project. Road expansion and improvement works are being carried out on a total route of 9.2 kilometers on the European and Asian sides.
The cost of the project is around $1.25 billion, according to data from official website of the project.
The Eurasia Tunnel is the latest in a series of key infrastructure projects in Istanbul including the city's third airport due to open in the second quarter of 2018.
In its first phase, the airport will have an annual capacity of 90 million passengers but will later have be able to handle 150 million travellers.
In August, Erdogan inaugurated the city's third bridge -- one of the longest suspension bridges in the world -- over the Bosphorus