Marmaray or B1 Commuter Train is a 76.6-kilometre-long (47.6 mi) commuter rail line located in Istanbul, Turkey. The line runs from Halkalı, on the European side, to Gebze, on the Asian side, along the north shore of the Sea of Marmara. Mostly using the right-of-way of two existing commuter rail lines, the Marmaray line linked the two lines via a tunnel under the Bosporus strait, becoming the first standard gauge rail connection between Europe and Asia. The two existing sections of the line were rebuilt and expanded from two tracks to three tracks, to allow for higher capacity with intercity and freight rail. The name Marmaray is a portmanteau of the words Marmara and Ray, which is Turkish for rail.