XINING -- An expressway opened Tuesday on the permafrost of Qinghai-Tibet Plateau, the world's highest plateau.

The 634.8-km expressway section, which connects Gonghe county with the city of Yushu in Northwest China's Qinghai province, was built at an average altitude of over 4,000 meters.

Up to 36 percent of the road is built on permafrost that could become unstable due to temperature changes caused by vehicles.

Advanced technology was developed to keep the ground surface stable for the construction and operation of the expressway, said Niu Jiangzhong, from the Electrical Engineering Co, Ltd of China Railway 12th Bureau Group.

Construction of the road took over six years, at a total cost of nearly 27 billion yuan ($4 billion).

To protect the local environment, vegetation was removed during construction and later replanted along the roadside.

The expressway has shortened the travel time between the provincial capital Xining and Yushu from 12 to just eight hours.