4.—(1) For the purposes of Article 3, a side car attached to a motor vehicle, if it complies with such conditions as may be specified in regulations made by the Department, is to be regarded as forming part of the vehicle to which it is attached and as not being a trailer.
(2) For the purposes of Article 3, in a case where a motor vehicle is so constructed that a trailer may by partial super-imposition be attached to the vehicle in such a manner as to cause a substantial part of the weight of the trailer to be borne by the vehicle, that vehicle is to be deemed to be a vehicle itself constructed to carry a load.
(3) For the purposes of Article 3, in the case of a motor vehicle fitted with a crane, dynamo, welding plant or other special appliance or apparatus which is permanent or essentially permanent fixture, the appliance or apparatus is not to be deemed to constitute a load or goods or burden of any description, but is to be deemed to form part of the vehicle.
(4) The Department may by regulations vary any of the maximum or minimum weights specified in Article 3.
(5) Regulations under paragraph (4) may have effect—
(a)either generally or in the case of vehicles of any class specified in the regulations; and
(b)either for the purposes of the provisions of the Road Traffic Orders[F1 and of the Offenders Order] and of all regulations made under those provisions or for such of those purposes as may be so specified.