I simply do not understand why the law as it stands now is insufficient to protect people from impaired drivers, at least insofar as any law can do so. Exactly what additional danger is posed now that wasn't posed before to justify a change in the law? If, in a given instance, the state cannot prove that a driver was impaired without a presumption to that effect, that driver obviously wasn't very impaired, were they? This is just another case of law and order authoritarianism versus liberty, which proponents of the former hate with all their being. Prima facie evidence of impaired driving should be EVIDENCE OF HOW THE DEFENDANT WAS DRIVING. Duh.