Last Wednesday was the end of China's "Golden Week", a one-week holiday. During that time millions of Chinese returned to the homes to enjoy time with their families.
The problem is too many of them came home on Tuesday. This is one reason why hundreds of thousands of motorists got stuck on the huge 50-lane highway between Beijing and Shenzhen.
If you watch the video taken from a drone, you will another reasons. The highway has a new checkpoint where it suddenly narrows from 50 lanes to 20.