The road they built stretched barely 6 kilometers, yet it twisted through 13 hairpin turns carved into a slope only a few hundred meters high. In places, 26 switchbacks seemed stacked almost on top of each other.

Locals had a saying: "Aizhai slope, mountains upon mountains, 13 turns — each turn, a gate to hell."

Traffic jams could last half a day, and accidents were frequent, sometimes fatal.

In 1992, the Aizhai traffic police squadron was formed. With no flat ground to stand on, the officers built a post in the trees — a few wooden planks nailed between branches, hanging over the cliff's edge. From this precarious perch, they directed traffic, suspended in midair.

By 2004, the provincial authorities had approved a new highway linking Jishou, the urban heart of western Hunan, to Chadong, a town located on the border with Chongqing.

But one challenge remained: they had to cross the Dehang Grand Canyon — a chasm more than 1,000 meters wide, with a 500-meter drop. They had to do it without destroying the fragile canyon ecosystem.