A train travels the Qinghai-Tibet route on May 13, 2011. The Qinghai-Tibet railway makes its way through a 550-kilometer section of permanently frozen earth, which posed the main threat to its safe operation. The railway has transported 23 million passengers with a record of 100 kilometers per hour through the frozen plateau and delivered goods of 120 million tons. The Qinghai-Tibet has been operating safely for five years. [Photo/Xinhua]