Extension line of Beijing-Zhangjiakou high-speed railway under construction

Photo taken on Dec. 17, 2017 shows the construction site of Zhengpantai tunnel of an extension line of the Beijing-Zhangjiakou high-speed railway in north China's Hebei Province. The 52-km extension of the Beijing-Zhangjiakou railway to Hebei's Chongli District, where most of the 2022 Olympic skiing events will be held, is expected to be completed by the end of 2019. (Xinhua/Yang Shiyao)