Northern Territory Consolidated Regulations Northern Territory Consolidated Regulations(1) A fifth wheel coupling used to connect a towing vehicle to a semi-trailer used in a B-double or road train must not be built with a pivot that allows a semi-trailer to roll relative to the towing vehicle.
(2) However, subrule (1) does not apply to a fifth wheel coupling if:
(a) the semi-trailer design requires torsional stresses to be minimised; and
(b) the roll axis of the fifth wheel coupling is above the surface of the coupler plate; and
(c) the degree of rotation allowed around the roll axis of the fifth wheel coupling is restricted to prevent roll instability.
(3) A trailer with only 1 axle group, or a single axle, (except a semi-trailer or a converter dolly) that is used in a road train must not have a coupling fitted at its rear.