Istanbul is one of the biggest metropolitans in the world with over ten million inhabitants. Increasing population and disposable income have led to an increase in the demand for transportation in daily life. Unfortunately, the demand for transport is met mostly by the increasing use of cars. As a result of that, environmental problems associated with the use of cars raise concerns. In order to tackle both urban traffic congestion and air pollution, local authorities and the government are investing in alternative modes for urban transportation to road transport modes. Of these, the most notable one is the Marmaray Project. In fact, this project is also one of the most interesting transport projects of the world. The aim of the project is to shift the demand from road transportation on the bridges over the Istanbul Straight to public transportation with rail systems. The project consists of five parts: a rail system from Gebze to Sogutlucesme, a bored tube system under the surface between Sogutlucesme and Uskudar on the Asian side of Istanbul, an immersed tunnel under the Istanbul Straight from Uskudar to Sirkeci, a bored tunnel under the surface between Sirkeci and Kazlıcesme and again a rail system from Kazlıcesme to Halkali on the European side of Istanbul. The objectives of the Marmaray Projects are various. It has been estimated that when the project has been completed, the number of passengers travelling by the rail system will dramatically increase and Istanbul will have an efficient urban public transport system, which will significantly contribute to policies taken to cope with urban traffic congestion and air pollution caused by traffic.