How did the train cross the herringbone line of Beijing-Zhangjiakou Railway?

As shown in the figure, the Beijing-Zhangjiakou Railway runs through the mountain between 1 and 3 from the lower right corner to the upper left corner of the figure.

The early buses passing through this section have two heads. First, the northbound train goes from 1 to 2, that is, Qinglongqiao Station, then the front end changes to the back end, the back end changes to the front end, and then goes backwards to 3. The herringbone railway can avoid digging tunnels.

Now, in order to increase the train flow, a herringbone railway has been built on the west side, called Qinglong Bridge West Station. The northbound train takes the West Station, and the southbound train takes the Old Qinglong Bridge Station.