3. Two signs shown in diagram 1 in the First Schedule or in diagram 1 in the Second Schedule shall be erected one on each side of the road at or as near as practicable to every point where a motor vehicle may duly pass from a length of road on which a speed limit is not in force to a length of road on which a speed limit is in force, which is a Class I road and the carriageway of which excluding any part thereof consisting of a central reservation or street refuge is at least thirty feet in width at that point:
Provided that where the length of road on which the speed limit is in force is a dual carriageway road one sign shall be erected on the left or near side of the road and one sign shall be erected on the central reservation instead of on the right or off side of the road.
4. Subject to the provisions of the last preceding paragraph, two signs shown in diagram 1 or diagram 2 in the First Schedule or in diagram 1 in the Second Schedule shall be erected one on each side of the road at or as near as practicable to every point where a motor vehicle may duly pass from a length of road on which a speed limit is not in force to a length of road on which a speed limit is in force:
Provided that where the length force is a dual carriageway road near side of the road and one sign instead of on the right or off side of road on which the speed limit is in one sign shall be erected on the left or shall be erected on the central reservation of the road.
5. Signs shown in diagram 3 in the First Schedule shall be erected in accordance with the provisions of the next succeeding paragraph along a length of road more than two hundred yards in length on which a speed limit is in force, not being a road on which a system of street lighting furnished by lamps placed two hundred yards or less apart is provided.
6. The signs mentioned in the last preceding paragraph shall be so erected along a length of road so mentioned that
(a) they face towards and are clearly visible to drivers of approaching motor vehicles;
(b) they are situated on each side of the road;
(c) the distance between any one sign on one side of the road and any sign next following that sign on that side and facing in the same direction does not exceed three hundred yards;
(d) the distance between any one sign on one side of the road and any sign next following that sign on the other side of the road and facing in the same direction does not exceed two hundred yards; and
(e) one such sign is not more than one hundred and fifty yards from each end of the said length of road:
Provided that where the said length of road is a dual carriageway road the foregoing provisions of this paragraph shall apply in relation to each carriageway on that length as though references in sub-paragraphs (b), (c) and (d') to "road" were references to that carriageway.
7. Two signs shown in diagram 4 in the First Schedule or in diagram 2 in the Second Schedule shall be erected one on each side of the road at every point where a motor vehicle may duly pass from a length of road on which a speed limit is in force to a length of road on which a speed limit is not in force:
Provided that where the length of road in force is a dual carriageway road one or near side of the road and one sign reservation instead of on the right or off on which the speed limit is not sign shall be erected on the left shall be erected on the central side of the road.
