This is one of the highest railways track in the world. It connects Xining, Qinghai Province, to Lhasa, Tibet Autonomous Region, in China. The total length of Qingzang railway is 1956 km. Construction of the 815 km section between Xining and Golmud was completed by 1984. This railway is the first to connect China proper with the Tibet Autonomous Region, which, due to its altitude and terrain, is the last province-level entity in mainland China to have a conventional railway. More than 960 km, or over 80% of the Golmud-Lhasa section, is at an altitude of more than 4,000 m. The 1,142-km Qinghai–Tibet railway from Golmud to Lhasa was completed on 12 October 2005. It opened to regular trial service on 1 July 2006. The trains are specially built for high altitude environment. From October 2006 five pairs of passenger trains run between Golmud and Lhasa, and one more pair between Xining and Golmud. The line has a capacity of eight pairs of passenger trains, and the carriages are specially built and have an oxygen supply for each passenger.