Tractor units

Tractor unit is a heavy-duty vehicle used to move semi-trailers. As a rule, tractor units have a fifth-wheel that couples tractor units to semi-trailers. Usually tractor units are powered by large displacement diesel engines.

The main advantage of tractor units usage is possibility to swap semi-trailers quickly, this way tractor units do not stand idle while the load is loaded or unloaded. Besides, unlike rigid trucks, tractor units are not restricted to one type of load as different types of semi-trailers can be swapped - tilt, tipper, tank, etc. There is one more tractor units advantage: load can be shared across several axles that makes all combination more manoeuvrable compared to same sized rigid trucks.

Tractor units are used in long-distance goods haulage and in international transportations. As a rule, they belong to the class of heavy goods vehicles (HGVs), although van based tractor units of smaller payload also exist.

The most common types of tractor units axle configuration are 4x2, 6x2 and 6x4. Three-axle tractor units usually have a lift axle that is raised to save tyres wear and increase traction when lightly loaded or running without a semi-trailer.

Tractor units are produced by all largest truck manufacturers in the world.