Road divided into two separate carriageways

The central reservation separates the two carriageways and the opposing directions of traffic. A driver uses the carriageway assigned to their direction, which is normally the one on the right relative to that direction, and then follows the lane-use rules within it. A crest does not change the general requirement to keep right. Moving close to the left-hand edge on a crest would reduce separation from opposing traffic or the central reservation and is not the correct rule.