17.For the purposes of calculating the number of axles, the word “axle” means any axle bearing or able to bear a load when the road vehicle or the combination of road vehicles is in motion, however many wheels are attached to it, with the exception of:
(1) the axles of any trailer whose load space is less than 4 m in length;
(2) the axles of a special mobile equipment trailer used solely for transporting the machinery, implements or fixtures with which it is permanently equipped;
(3) the axles of a camping trailer, other than a motor home whose use requires a special travel permit;
(4) the axles of a registered motor vehicle drawn by that vehicle or combination of road vehicles;
(5) the axles of a trailer transporting only road vehicles authorized to be operated mainly on a public roadway;
(6) the axles of a trailer used for purposes other than commercial purposes.