BEIJING, June 30 (Xinhua) -- China has solved three major difficulties to rewrite the world's history of railway construction with the completion of Qinghai-Tibet Railway, a railway official said Friday.

    The three difficulties are frozen tundra, high altitude and plateau environmental protection, said Zhu Zhensheng, vice director of the Ministry of Railways office in charge of the new line.

    About 550 kilometers of the tracks run on frozen earth, the longest in the world's plateau railways, posing great challenges for designing and construction, he said.

    The oxygen content along the railway is only 50-60 percent of that at sea level as 960 km of tracks are located at more than 4,000 meters above sea level, Zhu said.

    The annual average temperature on the Qinghai-Tibet Plateau is below zero degree Celsius with the minimum temperature at 45 degree Celsius below zero.

    None of the hundreds of thousands of workers died of altitude sickness in the past five years, making a medical miracle, said Professor John West with the School of Medicine, University of California, San Diego.

    More than 600 doctors and nurses served for the construction project and there was one clinic every 10 kilometers along the line, making sure that any sick worker could get medical treatment within 30 minutes.

    However, when the country built a highway between Qinghai Province and Tibet in early 1950s, almost the construction of every one kilometer of the road would claim one death.

    Thanks to the high altitude and harsh climate, the environment is very fragile along the railway. China has put environmental protection on the top of its agenda in the construction of the altiplano railway and workers built 33 passages for migrating animals.

    Endangered Tibetan antelopes are getting used to the railroad, said officials with the Hoh Xil National Nature Reserve Administration.

    A first batch of 67 pregnant antelopes from the eastern part of the reserve crossed Wubei bridge of the railway on May 16 to give birth in the hinterland, according to Gelai, head of Wudaoliang station in the Hoh Xil reserve.

    About 1,000 antelopes have crossed the railway via the special passages so far, Gelai said.

    "Tibetan antelopes started migrating earlier this year than the past few years. They no longer hesitate and cross the railway with ease," said Cega, director of the reserve administration in Qinghai Province.

    Rangers and volunteers in the Hoh Xil reserve also stopped vehicles on highways when they found antelopes were crossing.

    The 1,956-kilometer-long Qinghai-Tibet railway is the world's highest and longest plateau railroad and also the first railway connecting the Tibet Autonomous Region with other parts of China.

    The Chinese government is to build three more railway lines in Tibet as extensions of the newly-completed Qinghai-Tibet Railway, which would link the Tibetan capital, Lhasa, with Nyingchi to the east, and Xigaze to the west, while the third will link Xigaze with Yadong, a major trading town on the China-India border.

    The new lines would be built in 10 years, and increase Tibet's total railway length to more than 2,000 kilometers. Enditem