A trailer is defined as a vehicle that is towed by a motor vehicle but possesses no independent motive power source of its own. It constitutes a combination comprising a single motor vehicle-such as a truck, a tractor unit, or a forklift-and one or more attached trailers. The cargo truck or tractor unit serving as the powered section of this "road train" is referred to as the "prime mover" (or towing vehicle), while the unpowered section being towed by the prime mover is designated as the "trailer." Trailers represent a vital category of vehicles in road transport; indeed, the utilization of road trains is regarded as one of the most effective, simple, and significant methods for enhancing economic efficiency. This mode of transport offers numerous advantages, including speed, maneuverability, flexibility, and safety, and facilitates the convenient implementation of sectionalized transport operations.
A trailer functions as a complete transport unit only when coupled with a tractor unit or another motor vehicle. A trailer in which the entire gross weight is borne by the trailer itself is classified as a "full trailer" (often simply referred to as a "trailer" in common parlance). Its defining characteristics are the absence of an internal power source, the capacity for independent load-bearing, and its reliance on another vehicle for propulsion. Fundamentally, a trailer is an unpowered road vehicle-designed and engineered to require towing by a motor vehicle for proper operation-utilized for the transport of passengers or cargo, or for specialized purposes.
Trailers are categorized into two main types-full trailers and semi-trailers-based on the method by which they connect to the towing vehicle. A full trailer is one that is towed by a prime mover and bears its entire gross weight independently; conversely, a semi-trailer is one that is towed by a prime mover, with a portion of its gross weight being supported by the prime mover itself.
