In this regulation:
"eligible vehicle" means a heavy vehicle or heavy combination that, together with its load (if any), is any of the following:
(a) a rigid truck fitted with a tandem axle group if—
(i) it is not towing another vehicle; or
(ii) it is towing a trailer that is fitted with a single axle group, tandem axle group or tri axle group towards the rear of the trailer, where both the truck and trailer are designed to carry vehicles on 2 or more overlapping decks;
(b) a heavy combination if—
(i) the prime mover is fitted with a single axle group or tandem axle group; and
(ii) the semitrailer is fitted with a single axle group, tandem axle group or tri axle group;
(c) a bus fitted with a single drive axle group or tandem axle group;
(d) a truck or bus with a six-tyred tandem axle group at the rear;
(e) a B-double if—
(i) the prime mover is fitted with a tandem drive axle group; and
(ii) the trailer is, or the trailers are, fitted with either a tandem axle group or tri axle group;
(f) a road train not longer than 36.5m long if—
(i) the prime mover is fitted with a tandem drive axle group; and
(ii) the semitrailer is fitted with either a tandem axle group or tri axle group; and
(iii) the converter dolly is fitted with a tandem axle group.