3. Engineering plant must be a wheeled vehicle, a track-laying vehicle or a wheel-track combination vehicle.
4.—(1) Any wheel of engineering plant which is not fitted with a pneumatic tyre of soft or elastic material must be fitted with a smooth tyre and have the edges rounded to a radius of not less than 12 millimetres and not more than 25 millimetres.
(2) But, in the case of plant which is a gritting machine designed for use (and used) for gritting frosted and icebound roads, any tyre of the gritting machine may be fitted with diagonal cross bars which—
(a)are of equal width (which must not be less than 25 millimetres);
(b)extend the full breadth of the tyre; and
(c)are arranged so that the distance between the adjacent cross bars is not greater than the width of the crossbars.
(3) A tyre is not to be taken to be of soft or elastic material unless the material—
(a)is continuous around the circumference of the wheel, or fitted in sections so that, as far as is reasonably practicable, no space is left between the ends of each section;
(b)is of a thickness and design that, as far as is reasonably practicable, minimises vibration when the vehicle is in motion; and
(c)is free from any defect which might in any way cause damage to the surface of a road.
5. Engineering plant which has wheels and may (in accordance with paragraph 21) travel on roads at speeds exceeding those specified for slow plant in paragraph 20, must be fitted with tyres marked with a load and speed rating that is greater than the maximum load and speed that the plant can achieve when used on roads under its own power.
6. Engineering plant that is designed and constructed to operate on roads at speeds exceeding 12 miles per hour must be fitted with a braking system that complies with regulation 16 of the Construction and Use Regulations.
7.—(1) Any other engineering plant must be fitted with—
(a)an efficient brake capable of braking the vehicle at the maximum weight permitted under paragraphs 17 to 19 when travelling at the maximum speed permitted by this Schedule; and
(b)an efficient parking brake capable of holding the vehicle stationary when necessary.
(2) In the case of engineering plant that is a motor vehicle propelled by steam—
(a)the requirements of sub-paragraph (1)(a) are to be treated as met if the vehicle has an engine capable of being reversed; and
(b)the requirements of sub-paragraph (1)(b) are to be treated as met if the engine can be set to hold the vehicle stationary.
(3) Where engineering plant cannot be fitted with a parking brake on account of the nature of the engineering operations that it is specially designed and constructed to carry out, the requirements of sub-paragraph (1)(b) are to be treated as met if suitable scotches (or similar devices capable of holding the vehicle stationary when necessary) are fitted.