A pair of rails were laid down at 5,072 meters above sea level in Tibet's Amdo Wednesday morning, making a new topnotch of the world's railways.

The track laying location at Tanggula Mountain Pass is 255 meters higher than the century-old record of world's railway altitude previously kept by Peru at 4,817 meters above sea level for its tracks from the Pacific coast up to Andes range.

The laying of two 25-meter-long rails, acknowledged a tough part of the Qinghai-Tibet Railway, "rewrites the world's history of railway construction," said Sun Yongfu, China's vice railway minister.

The whole project extends 1,142 kilometers on the Qinghai-Tibet Plateau, dubbed the "roof of the world".

Linking Gelmud of Qinghai with Lhasa, Tibet's regional capital, the railway also boasts the world's highest railway station at 5,068 meters above sea level and the world's highest channel on frozen earth at 4,905 in elevation.

With an average altitude of 4,500 meters, it is undoubtedly the world's most elevated railway, of which 960 kilometers locate 4,000 meters above sea level.

High altitude and lack of oxygen, however, bring world-class enigmas for constructors.

About 550 kilometers of the railway runs on frozen earth, which "poses a major challenge to the railway construction," said La Youyu, deputy director-general of the headquarters for the Qinghai-Tibet Railway construction. 

"Frozen earth is vulnerable to climate change, which will thaw in summer and distend the railway base in winter, " La said.

To avoid possible dangers, the deputy director-general said, designers of the railway used technology of heat preservation, slope protection and roadbed ventilation in frozen earth areas.

With its advanced solutions to the tough problems in plateau railway projects, the Qinghai-Tibet Railway, however, provides a model for railroad construction in frozen earth areas, said Zhang Luxin, an expert with the Chinese Academy of Sciences.

Upon completion later this year, the maximum train speed in the frozen earth areas is designed to reach 100 kilometers per hour and 120 kilometers per hour on non-frozen earth in actual operation, Vice-Minister Sun said, noting it as "the most speedy for railways in frozen earth areas".

The gigantic Qinghai-Tibet Railway project was launched in June, 2001, and so far 22.64 billion yuan (about US$2.8 billion) was invested into the project. 

(Xinhua News Agency August 25, 2005)