The first railway to Tibet is ready to start operation this weekend, using sealed, oxygenated cars to cope with the thin air and high-tech cooling to keep the frozen track bed stable, China's Railway Ministry said Thursday.

The $4.2 billion rail line, which took four years to build, links Tibet's capital of Lhasa to Golmud, a small city in Qinghai province already connected to China's vast rail network.

China says the prestige project, which leaders have dreamed of realizing since the 1950s, will help economically develop the poor, restive western region and establish better trade and information links with the prosperous east.

Critics say it is part of a larger campaign by Beijing to crush Tibetan culture by allowing a huge influx of Han Chinese migrants.

The line will "hugely boost local development and benefit the local people," said Zhu Zhensheng, vice director of Railway Ministry's Tibetan Railway Office.

However, he acknowledged that few ordinary Tibetans would benefit directly from the railway — a key complaint by human rights and Tibet activists.

"At first there will be not very many opportunities for Tibetans to work on the train," he said at a briefing. "We hope to increase those opportunities."

Members of Students for a Free Tibet and pro-independence activists have been wearing black armbands in protest and say they will demonstrate at Chinese embassies and consulates around the world on Saturday.

"China's railway to Tibet is not meant to benefit Tibetans and is only meant to consolidate Beijing's control over the region," the group said on its Web site.

Human rights groups say the Chinese government limits numbers of monks in Tibetan monasteries, restricts religious teaching and requires monks to attend political classes and denounce the Dalai Lama.

Many Tibetans say their territory was independent when communist troops arrived in 1950 and the Dalai Lama has campaigned for autonomy to protect its culture. Beijing says Tibet has been part of China for centuries and accuses the Dalai Lama of agitating for independence.

The first passenger train to use the line is to leave Beijing on Saturday night and arrive in Lhasa, the Tibetan capital, 48 hours later on Monday.

The government says it hasn't decided whether to run daily train service.

The railway, sometimes referred to as the "Sky Train" in Chinese, is the world's highest, crossing mountain passes more than 16,500 feet high at speeds of 60 mph.

Peru's Lima-Huancayo line claimed the highest record previously, rising to above 15,748 feet.

About 80 percent of the Qinghai-Tibet line is above 13,000 feet and is laid on potentially unstable permafrost, or frozen ground.

To keep the permafrost stable, engineers sank pipes with cooling elements into the ground around the tracks to stabilize the embankments and ensure they stayed frozen.

"It's kind of like non-electric refrigeration," Zhu said.

Daniel Wong, a Shenzhen-based engineer who helped set up a similar cooling technology on permafrost along the Alaskan oil pipeline in the 1970s, said the pipes likely use solar energy to power a pump and compressor that continuously cycles ammonia or some other liquid into a gas, producing cold air.

He added that some 75 miles of the rail line were also put on elevated bridges in spots where the permafrost was thought to be least stable.

The train cars, manufactured by Canada's Bombardier Inc., have double-paned windows with ultraviolet filters to protect people from the sun's glare and were designed to regulate oxygen levels as the altitude changes, said Zhang Jianwei, Bombardier's China representative.

Zhang said passengers who experience breathing difficulties at high altitudes can breathe air with richer oxygen content provided in the coaches.