(180629) -- GOLMUD, June 29, 2018 (Xinhua) -- A maintenance worker checks the tracks at the Xinguanjiao Tunnel, the world's longest plateau rail tunnel, along the Qinghai-Tibet Railway in northwest China's Qinghai Province, June 27, 2018. With a length of 32.6 kilometers, the tunnel was put into operation at the end of 2014. (Xinhua/Hou Deqiang)(mcg) - Stock Image