During winter in low temperatures, when the steam locomotive stops for a while, the rails freeze and become slippery. It then becomes hard to shift the 364 metric tons of coal in the 13 self-turning cars, and they can only be moved by inching forward and back.

"I operate the accelerator and the brake entirely by touch. It requires years of practice," Cheng said.

At a speed of only 30 km/h, it takes an hour for the train to reach the mining zone. Cheng and his colleagues have some time to relax while the coal is loaded.

"I will be retiring in December. How time flies. I'm already 55. I've spent more time with this machine than with my wife. It's time to say goodbye," he added.