The Gokarla Tunnel, a key section of a highway connecting Lhasa and Lhokha in the Tibet autonomous region, was completed on Wednesday after seven years of construction. [Photo provided to chinadaily.com.cn]

A highway tunnel connecting Lhasa with Zhanang county in the Tibet autonomous region was completed on Wednesday after seven years of construction, marking big progress on another vital traffic corridor in the region.

The Gokarla Tunnel starts at Dechen township in Lhasa's Dagze district and ends at Samye township in Zhanang county of Lhokha. It is a key section of the Lhasa-Tsethang Highway (S5), helping complete a one-hour economic zone in the central part of the region, according to the builder, CCCC Second Highway Engineering Co.

The altitude at the entrance of the tunnel is 4,248 meters; the exit is 4,117 meters above sea level.

With lanes measuring nearly 13,000 meters, the tunnel is said to be super long.

Zhou Xiaobing, the project leader, said the average altitude of the tunnel is 4,300 meters, with complex geological conditions along the way.

"During construction, difficulties arose in excavation, long-distance ventilation, large inclined shaft slopes, lack of oxygen on the plateau, cold weather and low temperatures," he said, adding that the geological challenges included excessive soil moisture content, rock bursts and gas poisoning.

Zhou said that if the project location were in a plains area, it would probably take a maximum four years to complete. But it's much more difficult in Tibet, where the average altitude tops 4,000 meters.

According to the company, comprehensive technological innovation was brought into play in response to construction difficulties. Advanced equipment was introduced, such as a three-arm rock drilling trolley, wet spraying manipulator, electric loaders and electric excavators.

"The use of this advanced equipment significantly reduced the number of workers needed and significantly improved construction efficiency and safety," Zhou said.

Linking the regional capital, Lhasa, with the region's southern city of Lhokha, the Lhasa-Tsethang Highway is expected to be operational by the end of this year. Travel time between the two cities will be reduced to about an hour from three hours previously.