There is no self-contained power unit for trailers or semi-trailers. The car train consisting of towing cars belongs to the automotive category.
The semi-trailer is a trailer that is positioned behind the center of gravity of the vehicle (when the vehicle is uniformly loaded) and is equipped with a coupling device that can transmit horizontal or vertical forces to the tractor. That is, part of the total weight of the trailer is taken by the tractor. Its characteristics: It has no power, it is carried together with the main vehicle, and it depends on the main vehicle towing the vehicle's drawbar trailer draw? bartrailer

The towbar trailer is a trailer with at least two axes and has: one axis can be steered; the tow bar moving through the angle direction is connected with the towing vehicle; the tow bar can move vertically and is coupled to the chassis, so it cannot bear any vertical force. Semi-trailers with hidden support are also used as towbar trailers.
Bus trailer trailer
Passenger car trailers are tow bar trailers for carrying people and their carry-on baggage on the design and technical features. It can be equipped according to 1.2.2 and 1.2.3.
Tow bar truck trailer goodsdraw?bartrailer
Towbar truck trailers are towbar trailers that are used to carry cargo on their design and technical characteristics.
General purpose drawbar trailer general purposedraw?bartrailer
A universal towbar trailer is a towable trailer that carries goods within an open (planar) or enclosed (bay) cargo space.
Special drawbar trailer sPEcialdraw?bartrailer
The special tow bar trailer is a tow bar trailer, used according to its design and technical characteristics as follows: special arrangements are required to carry personnel and/or cargo; only certain prescribed transport tasks are performed (eg passenger car transport trailers, Fire trailers, low flatbed trailers, air compressor trailers, etc.).