The Trans-Mongolian Railway links Ulan-Ude on the Trans-Siberian Railway in Buryatia, Russia, with Jining in Inner Mongolia, China, via Ulaanbaatar, the capital of Mongolia. It was completed in 1956 and runs from northwest to southeast, with major stations at Naushki/Sükhbaatar on the Russian border, Darkhan, Ulaanbaatar, Choir, Sainshand, and Zamyn-Üüd/Erenhot on the Chinese border. There are important branch lines to Erdenet and Baganuur.

Choir is a city in east-central Mongolia. It is the capital of Govisümber Province. Choir is officially known as Sümber sum.