In paragraph 5(1) of Part I of Schedule 4 to the 1972 Act (special types of vehicle), for the words “an unladen weight exceeding 1,525” there shall be substituted the words “a relevant maximum weight or a relevant maximum train weight exceeding 3,500 kilograms or, in the case of a vehicle which has neither a relevant maximum weight nor a relevant maximum train weight, a design weight which exceeds 3,500”