3. In this Order “abnormal indivisible load vehicle” means a vehicle of any of the following descriptions—
(a)a motor vehicle of category N3 specially designed and constructed for the carriage of abnormal indivisible loads;
(b)a trailer of category O4 specially designed and constructed for the carriage of abnormal indivisible loads;
(c)a locomotive specially designed and constructed to tow trailers falling within sub-paragraph (b); or
(d)a motor vehicle of category N3 which is not constructed itself to carry a load but which is specially designed and constructed to tow trailers falling within sub-paragraph (b).