Marmaray is a suburban line improvement project, whose foundations were laid in 2004 and its construction continues, and will connect the European and Asian sides under the Bosphorus. It is completely different from Ankaray and Bursaray, which are the inspiration for its name. Because Ankaray and Bursaray are both subways. Marmaray is a Eurotunnel-like railway project in the English Channel. However, it has connections to the Istanbul metro.
When the construction is completed, the line connected to Marmaray has a 16 km Bosphorus crossing and on the European side. Halkalı- Yenikapı is planned to be approximately 76 km long, on the Anatolian side, between Gebze and Harem. Railways on different continents will be combined with immersed tube tunnels under the Bosphorus. The Marmaray Project will have the deepest immersed tunnel in the world with 60 meters.