Heavy Vehicle (Vehicle Standards) National Regulation

A fifth wheel coupling used to connect a towing vehicle to a semitrailer used in a B-double or road train must not be built with a pivot that allows a semitrailer to roll relative to the towing vehicle.

However, subsection (1) does not apply to a fifth wheel coupling if—

the semitrailer design requires torsional stresses to be minimised; and

the roll axis of the fifth wheel coupling is above the surface of the coupler plate of the coupling; and

the degree of rotation allowed around the roll axis of the fifth wheel coupling is restricted to prevent roll instability.

A trailer with only 1 axle group or a single axle, other than a semitrailer or a converter dolly, that is used in a road train must not have a coupling fitted at its rear.