Cheng waited for an hour before the signal light came on and the train clattered toward the mine.

Without any assistance from computers or smart driving systems, locomotive drivers must stick to one fundamental principle－stay alert. Cheng and Ma opened windows on each side of the train and leaned out as far as they could to take a close look at the environment around the tracks.

Behind them, Dai kept shoveling coal into the furnace. Liu Xiaozhi waved his flags, red for stop and green for go.

"I've been driving on these tracks for 23 years. Every turn and curve is ingrained in my heart. But every time I drive, I have to look out of the windows to check the turns just to be safe," Cheng said.