Marmaray, the 77-kilometer urban rail commuter project to connect Asia to Europe beneath the Istanbul Strait, will connect Halkali on the European side of the city with suburban Gebze on the Asian side.
The project is planned to sharply reduce the travel time and help relieve the city of the growing traffic congestion.
The rail system will carry 150,000 passengers per hour on both sides and link with the municipal light-rapid rail system and subway.
The tender to procure 440 cars was the last procurement of the project, officials said.
The last tubes of Istanbul's 60-meter deep underwater tunnel were connected last week.