The semi-trailer tractor is a commercial vehicle equipped with special devices for towing semi-trailers, which are towed by the tractor. The semi-trailer is a trailer with its axle placed behind the center of gravity of the vehicle (when the vehicle is uniformly loaded) and equipped with a coupling device that can transfer horizontal or vertical forces to the towing vehicle! Generally, a full trailer has two axles and a semi-trailer has one axle. The semi-trailer refers to a vehicle that has no power and relies on the traction of the main vehicle to carry it together with the main vehicle. The semi-trailer is connected to the traction seat of the tractor through a traction pin, and a common container transport vehicle is a typical semi-trailer train, with the rear loading part being the semi-trailer.