1. In this Regulation, “axle spread” means the longitudinal distance between the centres of the foremost and rearmost axles of an axle unit; “bed length” means the external measurement of a trailer from the front of its cargo carrying space to the rear of its cargo carrying space, but excluding any portion of auxiliary equipment or machinery that extends beyond the front of the trailer and that is not designed for the transportation of goods; “effective overhang” means the longitudinal distance from the turn centre of the trailer to its rearmost point, including any load; “fifth wheel assembly” means a plate-type coupling device comprised of a kingpin, locking jaws and plates whose lower half is mounted on the rear portion of a vehicle frame or the frame of a trailer converter dolly and whose upper half is fastened to the underside of the forward portion of a semi-trailer for the purpose of supporting and towing the semi-trailer; “full trailer” means a trailer designed so that its own weight and any load are carried on its own axles and includes a combination consisting of a semi-trailer and a trailer converter dolly; “inter-axle spacing” means the longitudinal distance separating two consecutive axle units within a vehicle or combination of vehicles, measured from the centre of the rearmost axle of the foremost axle unit to the centre of the foremost axle of the other axle unit; “liftable axle” means an assembly of two or more wheels whose centres are in one transverse vertical plane that is equipped with a device for altering (other than by longitudinal movement of the assembly only) the weight transmitted to the highway surface and that may be able to lift its tires from contact with that surface; “self-steering axle” means an assembly of two or more wheels whose centres are in one transverse vertical plane and whose wheels can articulate in response to forces generated between the tires and the road or through mechanisms and linkages that operate independently of the driver; “swing radius” means the greatest horizontal distance from the vertical axis through the centre of the kingpin to any point on the semi-trailer ahead of the kingpin, including load and any extension to the length caused by auxiliary equipment or machinery; “tandem axle” means a “dual axle” as defined in Part VIII that does not include a liftable axle or a self-steering axle and that has the same number of tires on each wheel; “track width” means the width of an axle across the outside faces of the tires measured at any point above the lowest point of the rim; “tridem axle” means a “triple axle” as defined in Part VIII that does not include a liftable axle or a self-steering axle and that has the same number of tires on each wheel; “turn centre” means the geometric centre of the axle unit on a semi- trailer or of the rear axle unit on a tractor or a full trailer; “wheelbase” means the longitudinal distance, (a) from the centre of the kingpin to the turn centre in the case of a semi-trailer, (b) from the centre of the front axle to the turn centre in the case of a tractor, (c) from the centre of articulation of the turntable to the turn centre in the case of a full trailer. O. Reg. 32/94, s. 1; O. Reg. 600/98, s. 1.