Restriction on the construction of rumble devices6.

Where a rumble device is constructed in a road—

(a)

no vertical face of any material forming that device shall exceed 6 millimetres measured vertically from top to bottom of that face; and

(b)

no part of the device shall be more than 20 millimetres above the surface of the carriageway;

provided that a measurement shall be deemed to comply if it is no more than 5 per cent or 1 millimetre, whichever is the greater, more than the corresponding measurement in this regulation.