For the coal transportation industry, the secondary and primary vehicles are not new, especially in the long-distance coal transportation, the secondary and primary vehicles are more common, and even have been widely existed in the early years.

The so-called parent vehicle refers to the large vehicle pulling the small vehicle. For example, both vehicles are one-way transportation. When the empty vehicle returns, one vehicle carries the other vehicle. In this way, "carrying the vehicle" can save part of the highway and fuel costs, which has played a certain role in reducing costs and increasing efficiency in the fierce competition environment.

In order to meet the market demand, many car enterprises have also made many updates to the parent car. They have not only improved the upper and size of the two cars, but also upgraded the cab of the parent car to a high roof double sleeper, providing sufficient rest space for the driver of the parent car; At the same time, the cab of the secondary vehicle is designed as a flat top type, which is convenient for getting on and off the vehicle. At the same time, it tends to be lightweight as much as possible to further reduce fuel consumption and deal with the high limit road section during transportation.

Although it sounds reasonable, strictly speaking, the parent car is a product that exploits legal loopholes. According to the requirements of laws and regulations, the auxiliary transport vehicle must use a special flat car. It is obvious that most of the secondary and primary vehicles on the market do not meet this requirement.

It was originally thought that the sub parent vehicle was the limit of the freight industry. However, the market did not stop at this point to maximize the transport benefits. An upgraded version of the sub parent vehicle, the Yesun vehicle, was also called "the third generation of the generation of grandparents" by some owners, which means that one vehicle carries two empty vehicles on the road at the same time.

The picture below shows a grandchild car being unloaded. Due to the problem of model and shooting angle, the whole car cannot be displayed in the same screenshot. This is a combination of three pictures. From the figure, we can also see the loading and unloading method of Yesun cars. One gets on and off from the back of the main cab and the front of the car, and the other gets on and off from the back of the main car.

While marveling at the loading method of Yesun truck, I have to marvel at the designer's thoughtful thinking. According to a promotional material on the Internet about Yesun car, the main car is 13.75m long, with corrugated blocks at the bottom and flower bars at the top. The height is 1m. It is very convenient to transport coal with tarpaulin; Two grooves are designed on the rear bottom plate of the main car compartment to reduce the height of the first secondary car. At the same time, a hopper is designed at the bottom of the groove, which is very convenient for coal unloading; Two grooves are also designed on the front high plate of the main car, which can reduce the height of the second car; The rear of the main car adopts an integral large door, which can also be matched with grooving and ladders; Such a main vehicle can carry two 9.5m models on the road at the same time. If three vehicles return empty, this way can save some fuel consumption and tolls. It sounds very attractive.

However, is such a car really worth advocating? Does the freight market really need such a diverse inner volume?

First of all, whether it is a parent vehicle or a grandchild vehicle, it is very dangerous to drive on the road, because the child vehicle itself is an independent large cargo, and its contact area with the parent vehicle is very limited, so the friction is not enough. If it is not fixed properly, once the inertial displacement occurs on the way, it is very easy to cause major traffic accidents, which is very harmful to drivers and other traffic participants. Although the purpose of transportation is to make money, it should be taken in a reasonable way. If life safety cannot be guaranteed, what's the use of making more money?

Secondly, it disturbs the market, causing the freight to drop again and again, thus falling into a vicious circle, which is not conducive to the long-term development of the freight market. Both the parent car and the grandchild car are the products of the market downturn. In the fierce competition and difficult survival environment, people have to find ways to reduce costs and increase efficiency. But everything must be done in a proper way. In the end, using illegal ways will only harm others and themselves. The toll and fuel costs have been saved, and the transportation cost has been reduced. Usually, the transportation cost is 10000 yuan, and these models can run for thousands of yuan. How can ordinary models compete for orders? We had to take the initiative to reduce the freight. In the long run, the originally low freight will be reduced by a large part. If there are many such models in the market, will the owner still pay high freight? Almost impossible.

Third, non-compliance. As we mentioned above, in a strict sense, the parent and child cars originally belong to the vehicle model of drilling holes, and the "car on the back" mode is easy to exceed the height limit. Even if the gooseneck trailer is used, it is also suspected of exceeding the height limit, let alone the grandchild car.

The owner may have said: I bought the parent car or the head office of the grandchild car with the correct size, right? Not super high, not super long, not overweight, is it compliant? It's not that simple.

According to GB7258-2017:

The cargo box (cargo box) shall be installed firmly and reliably, and the structure and device for heightening, lengthening and widening the cargo box (cargo box) shall not be set in the design and manufacturing.

The cargo position of the cage type cargo vehicle shall be cage type or fence type. The top of the loading part shall be installed with a ceiling bar which is fixed to the side fence and cannot be disassembled and adjusted; The longitudinal distance between ceiling poles shall be no more than 500 mm.

For the convenience of getting on and off the slave cars, the tailgate pillar of many main cars will be designed as a pull type, or the upper part of the barn grille will be designed as a folding type and a detachable type. The above two items alone will probably block a large number of slave cars or grandchild cars out of the laws and regulations.