I think if there is a significant risk of drivers going down the wrong carriageway, additional or larger regulatory signs should be considered, rather than the informatory diag. 818.
What about a larger or higher 610 ‘keep left’ arrow at the start of the central reserve, and/or a pair of 616 ‘no entries’ on the wrong carriageway? Or possibly double while lines or hatching to keep traffic on the correct side of the road before the DC starts? All just ideas that may or may not work for your particular situation.