The Trans-Mongolian Railway connects Ulan-Ude on the Trans-Siberian Railway in Buryatia, Russia, with Ulanchab in Inner Mongolia, China, via Ulaanbaatar, Mongolia. It was completed in 1956, and runs from northwest to southeast with major stations at Naushki/Sükhbaatar on the Russian border, Darkhan, Züünkharaa, Choir, Sainshand, and Zamyn-Üüd/Erenhot on the Chinese border, where the railway changes from single-track to double-track and its gauge changes from 1,520 mm Russian gauge to 1,435 mm standard gauge. The railway also has important branch lines to Erdenet and Baganuur.