Mechanic Tan Xu walks to the next train to inspect at a depot in Xining, northwest China's Qinghai Province, on Jan. 8, 2020. Tan Xu begins his 12-hour shift at 8 pm. He makes an inspection of the trains in the depot every two hours, to make sure that the temperature in trains remains above 18 degrees Celsius so they are fully functional during their trips. (Xinhua/Zhang Long)