The Marmaray project is one of the crucial transportation projects in the world. Credit: International union of railways.
Five Tunnel Boring Machines have been used during the construction of the Immersed Tube Tunnel. Credit: International union of railways.
The structural works at Uskudar, Yenikapı and Kazlıçeşme station was completed by January 2013. Credit: International union of railways.
The NATM excavation works at the platform and cross over tunnels were completed by January 2013. Credit: International union of railways.
The Marmaray project also included the upgrade of the commuter rail system in Istanbul. Credit: International union of railways.

The Marmaray railway engineering project is a 76.3km rail link that was inaugurated in October 2013 on the 90th anniversary of the Turkish Republic.

The rail line was used by more than 24 million people until May 2014.

Construction work was scheduled to be completed in April 2009, but this was revised to 2010. The opening of the Marmaray Rail Tube Tunnel and Commuter Rail Mass Transit System was delayed due to archaeological discoveries made at the Yenikapi construction site.

The first phase involved a  rail tunnel beneath Bosphorus (Istanbul Strait), which represents the first physical rail link between Europe and Asia. Opened in March 2019, the second and main phase included Halkali-Gebze suburban line, which connects Halkali in Europe and Gebze in Asia.

Forecasts estimated that by 2025, 1.7 million trips per day will be made on the new route. The travel time for the 76.3km stretch is 81 minutes.

The Marmaray railway engineering project

The city of Istanbul saw heavy road traffic, pollution and limited high-capacity transport systems. The Marmaray project, apart from cutting pollution, significantly aided the development of the railway system in Turkey, which completed its first high-speed railway line linking the capital city Ankara with Istanbul, ultimately reducing journey times by more than three hours between these two major population centres.

The Marmaray project, 76.3km (48 mile) high-capacity metro style railway, provides mass transit for the city’s population. It connects Europe and Asia by crossing the Istanbul Strait. The project included upgrading 63km (40 miles) of suburban railway, and purchasing new rolling stock to provide the service.

Following more than a decade of studies, a funding agreement was struck in 1999 between the Republic of Turkey and the Japanese Bank for International Cooperation. This brought together 35% of the total project funding and allowed the underwater tunnel to be constructed. The total project cost was estimated at $4.5bn.

There were four main components of the Marmaray Project: the underwater railway tunnel, improvement of the Gebze-Haydarpasa and Sirkeci-Halkali suburban railway lines, electrical and mechanical works, and the procurement of new rolling stock. With the opening of the tunnel, commuter trains have started operating from Ayrılıkçeşme station (Asia) to Kazlıçeşme station (Europe).

The project was financed by the Japan Bank for International Cooperation (JBIC) and the European Investment Bank (EIB). JBIC lent $950m under a long-term low-cost loan while EIB provided a €650bn soft loan.


The Marmaray railway engineering project involved the construction of a tunnel under the Istanbul Strait. The idea was first mooted in 1860 but the depth of the water negated using traditional seabed, or below, tunnelling methods.

The tunnel was considered to be the deepest immersed structure in the world, 55m below sea level. Its length is 13.6km (8.5 miles) long with 9.8km of bored tunnel, 2.4km built using cut-and-cover methods and the remaining 1.4km as a tube tunnel.

The tube tunnel consists of two running lines separated by a dividing wall, pre-cast in lengths of around 100m before towing into place across the sea and dropped into place for joining together and dewatering. This process caused the water pressure at the other end of the section to compress a rubber sealing gasket, making the joint watertight. Foundations were below each section once they were lowered into place, replacing temporary foundations.

The immersed tunnel is connected to the shore by tunnels bored using tunnel boring machines (TBMs) to produce separate bores for each running line, with connections at frequent intervals for emergency use.

The scheme also included the upgrading of 63km of existing suburban railway lines, rebuilding 37 stations and building three new ones. Platforms are 225m long, the equivalent of 10 carriage lengths. The stations are based on metro style operations but are also served by heavy rail trains capable of travelling at 100km/h (60mph) with an average speed between stations of 45km/h (28mph).

The Marmaray project provides an east-west transport corridor with a connection at Yenkapi to the north-south metro line.

Rolling stock

Hyundai Rotem was awarded a contract for supplying 440 rail sets for the project in 2008. The first batch of 160 cars was delivered in 2011, the second was delivered in September 2013.

The new trains have a maximum design speed of 105km/h (65.24mph).

Signalling and communications

Signalling and communications form an important part of the new route to meet the demands of safely transporting 75,000 passengers per hour in the future with intensive operations.


The entire project was supervised by State Railroads, while the Ports and Airports Administration oversaw the project.

The construction contract was assigned to a Japanese-Turkish consortium led by Taisei. The firms in the consortium include Kumagai Gumi of Japan, Gama Endustri Tesisleri Imalat ve Montaj and Nurol Construction and Trade of Turkey.

Bechtel and Turkey’s Enka won a €1.48bn ($1.92bn) contract to upgrade the existing railway line in Gebze and Halkali district and another line passing through the tunnel. The joint venture of Invensys Rail and Spanish-based OHL won a €195m ($254.08m) contract to supply signalling and communication solutions for the project. Transport Design International (TDI), an interior and exterior design firm, provided rolling stock designs for Hyundai Rotem.

Siemens Mobility installed and commissioned the signalling and control system, SCADA systems, and CBTC and ERTMS technology on the Gebze-Halkali rail line.