The roads authority may construct and maintain works in the carriageway of a public road—
(a)along any length of the road for separating a part which is to be used by traffic moving in one direction from a part which is to be used (whether at all times or at particular times only) by traffic moving in the other;
(b)at junctions of the road for regulating the movement of traffic; or
(c)for providing places of refuge for the protection of pedestrians crossing the road.