What does it mean to write Du Dong on the train and then go from Guiyang to Wenzhou?

According to what you said, it means this is a sports car. The task of this train is completed, and the next train is ready after returning to the warehouse. This can not only save train resources, but also ease the capacity of other trains in the same section. Because the running of a sports car is a "big trap and small circle", once one of the responsible trains fails to reach the finish line on time and the preparation time is short, the next train it takes will also start late. This is a good understanding of what a sports car is. Here are some examples of sports cars. The first one is called the water sign, but now most of them have been replaced by the train running interval signs shown below. The following picture is from the train bar, thanks to the original author for the picture.