4.—(1) This regulation has effect for the purpose of defining in relation to a vehicle what part of the vehicle is to be regarded as the front of the vehicle for the purposes of section 15(1) of the Act and these Regulations.
(2) Subject to paragraph (3), every part of the vehicle forward of the transverse vertical plane passing through the rearmost part of the driver’s seat shall be regarded as the front of the vehicle; and accordingly no part of the vehicle to the rear of that plane shall be regarded as being in the front of the vehicle.
(3) Where a vehicle has a deck which is above the level of the driver’s head when he is in the normal driving position, no part of the vehicle above that level shall be regarded as being in the front of the vehicle.