This Regulation applies to motor vehicles of categories M1 and N1 . However, vehicles of category N1 where the driver’s position "R-point" is either forward of the front axle or longitudinally rearwards of the front axle transverse centreline by a maximum of 1,100 mm, are exempted from the requirements of this Regulation. This Regulation does not apply to vehicles of category M1 above 2,500 kg maximum mass and which are derived from N1 category vehicles, and where the driver’s position "R-point"is either forward of the front axle or longitudinally rearwards of the front axle transverse centreline by a maximum of 1,100 mm; for these vehicle categories Contracting Parties may continue to apply the requirements already in force for that purpose at the time of acceding to this Regulation.