Different classes of traffic may be prescribed by a scheme under section 7 of this Act in relation to different parts of the special road to which the scheme relates.

The classes of traffic prescribed by any such scheme shall be prescribed by reference to the classes set out in Schedule 3 to this Act.

The Secretary of State may by order vary the classes of traffic specified in the said Schedule 3 and the composition of any such class; F1 . . .

A variation order may contain provision applying the variations made by the order to existing schemes (whether made by the Secretary of State or a local roads authority); and in the absence of such provision a variation order does not affect the classes of traffic prescribed in an existing scheme.

In subsection (4) above an “existing scheme” means a scheme under section 7 made before the order comes into operation.