There is another problem with that suggestion. The signs round Marine Drive regularly get stolen for their scrap value and it would be a case of continuous replacement.
The actual number of cars one finds travelling the wrong way is quite small and is generally the ones who miss the no entry signs at the West Shore end. I am excluding those delivery vans and yobs who deliberately choose to travel the wrong way. The worst offenders are cyclists who seem to thing that he no entry sign does not refer to them.
I cannot recall any accidents due to these situations, but then someone may be able to tell me otherwise.