The Istanbul Strait Road Crossing project is a crossing of the Bosphorus Strait, connecting the European and Anatolian regions of Türkiye and relieving congestion and traffic pressure on Istanbul’s existing Bosphorus Bridges. 

The tunnel was constructed between the areas of Kazlicesme and Goztepe, along a 14.6-km route and featuring a 5.4-km twin-deck tunnel that crosses the Bosphorus beneath the seabed.

The project included the construction of an additional 10km of access roads, two toll plazas and the operations buildings for the tunnel. The project reduced the travel time between Kazlicesme and Goztepe from 100 minutes to just 15 minutes.

Arup began working on the award-winning project in 2009, providing technical advisory, environmental monitoring and traffic audit services to the institutions funding the project during the procurement and construction stages. The tunnel brings two continents together, linking Europe with the motorway network on the Asian side. Representing a truly international effort with investors from Türkiye and South Korea, the tunnel materials were provided from Germany, and operation, surveying and maintenance was assisted by France, Italy, Netherlands and the UK.

Major consultancy services

Arup advised the funding institutions on the technical requirements for the project, including a review and commentary on the design, the traffic models and economics, the construction and operation proposals, the environmental impact and stakeholder consultations and the review of construction costs, contract documents and analysis of the project risks including seismic risk.  

The tunnel opened to the public in December 2016

The finished tunnel stands about 1km south of the undersea train tunnel Marmaray and marks another success for Turkish infrastructure. 

While significantly improving commuting times for citizens and businesses in Istanbul, the tunnel also reduces the cities air and noise pollution.