Why Almost No Railway Can Cross This Mountain — Except China's

At 5,072 metres, China's Qinghai–Tibet Railway is the highest railway on Earth. Along roughly 550 kilometres of its route, though, the real obstacle was never the mountains. It was the ground. The line crosses permafrost that sits less than a degree below freezing, and an ordinary embankment warms that ice until it melts and the track sinks. The highway beside it has been cracking for decades. Railways built on permafrost elsewhere have all reported frost damage on more than 30 percent of their track.

In the mid-1980s, Paul Theroux wrote that the Kunlun Range was "a guarantee that the railway will never get to Lhasa." Work on the line had started in 1958 and stopped twice. When China tried again, engineer Cheng Guodong argued that insulation would fail, and that the only way to keep the ground solid was to cool it. So the railway has to refrigerate itself, with steel thermosyphon pipes, beds of broken rock and long bridges, and it gets no electricity to do it.

This video covers why the plateau beat everyone for a century, how the cooling system works, what it cost, and whether it can keep up as the climate warms.

Sources: Paul Theroux, Riding the Iron Rooster; Beijing Review; The Guardian (Jonathan Watts, 2005); Cheng Guodong, Chinese Academy of Sciences; 2008 roadbed-cooling paper with the Qinghai–Tibet Railway construction headquarters.