(1) The National Roads Authority may apply, or cause to be applied, by automated means or otherwise, to any national managed road or any part, carriageway or lane thereof, a special limit (referred to in this Act as a 'variable speed limit') being a speed limit of -

(a) not less than 20 kilometres per hour, and

(b) not more than the speed limit otherwise provided or having effect under this Act,

as the speed limit for mechanically propelled vehicles on that national managed road, part, carriageway or lane, in lieu of the speed limit provided or having effect under this Act by displaying the speed limit, or causing it to be displayed, electronically on a traffic sign above or to the side of the national managed road, or part, carriageway or lane thereof.

(2) A variable speed limit is in force for the period during which it is displayed in accordance with subsection (1).

(3) The speed limits that may be applied under this section are -

(a) 20 kilometres per hour,

(b) 30 kilometres per hour,

(c) 40 kilometres per hour,

(d) 50 kilometres per hour,

(e) 60 kilometres per hour,

(f) 70 kilometres per hour,