Knowra Semi-trailer truck Semi-trailer truck A road vehicle consisting of a powered tractor unit coupled to a semi-trailer. The trailer’s front rests on the tractor, while its rear is supported by its own wheels.
Fifth-wheel coupling : A pivoting plate on a tractor unit that couples to the kingpin beneath a semi-trailer. It connects the units while allowing the trailer to turn relative to the tractor.
Diesel engine : An internal-combustion engine that ignites fuel through compression rather than a spark. Diesel engines commonly provide the sustained pulling power used by tractor units.
Dry van : An enclosed, non-refrigerated trailer used to carry freight protected from weather. It is a common trailer configuration for general packaged cargo.
Full trailer : A trailer whose front and rear are supported by its own axles and which is towed by a vehicle. Unlike a semi-trailer, it does not rest on the towing vehicle at its front.
Kingpin : A steel pin beneath a semi-trailer that locks into a tractor’s fifth-wheel coupling. This pin is the trailer’s side of the central coupling.
Air brake : A braking system that uses compressed air to apply force at vehicle brakes. Air lines connect tractor and trailer braking systems in many heavy combinations.
Refrigerated trailer : An insulated trailer equipped to maintain controlled temperatures for transported goods. It adapts the combination to food, medicine, and other temperature-sensitive freight.
Rigid truck : A truck with its cab, powertrain, and cargo body mounted on one continuous chassis. Its cargo body is not a separately coupled semi-trailer.
Tractor unit : The powered front vehicle in a tractor-trailer combination, equipped to pull a semi-trailer. Its engine, cab, axles, and fifth wheel provide the combination’s power and support.
Axle : A shaft or assembly that supports vehicle wheels and transmits loads or driving force. Axles carry the tractor and trailer’s weight and may transmit engine power.
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