21.—(1) A special type agricultural vehicle that is a track-laying motor vehicle may be used on roads only if the tracks operate on rubber or an alternative composite material that does not damage the road surface.
(2) The overall width of a special type agricultural vehicle together with the width of any lateral projection or projections of any load carried on it must not exceed 4.3 metres.
(3) For the purposes of paragraph (2)—
(a)the overall width of a special type agricultural vehicle that is a motor vehicle towing an agricultural trailer or agricultural trailed appliance in an offset manner, is to be taken as the overall width of the motor vehicle and trailer (or trailed appliance) measured as if they were one vehicle; and
(b)where any agricultural implement is rigidly (but not permanently) mounted on a special type agricultural vehicle, any part of the implement that extends beyond a side of the vehicle is to be treated as a lateral projection, regardless of whether any part of the weight of the implement is transmitted to the surface of the road otherwise than by the wheels or tracks of the vehicle.
(4) The gross weight of a special type agricultural motor vehicle that is a track-laying vehicle, together with the weight of any load carried on it, must not exceed 30,000 kilograms.
(5) All spikes, cutting blades or other protruding sharp appliances that are fitted to or mounted on a special type agricultural vehicle must be removed or effectively guarded so that no danger is caused (or likely to be caused) to any person.
(6) A special type agricultural vehicle must not at any time travel at speeds exceeding—
(a)20 miles per hour in any case where the overall width of the vehicle is more than 2.55 metres but less than 3.5 metres;
(b)12 miles per hour in any case where the overall width is 3.5 metres or more.